Method and device for encoding and decoding image signal

ABSTRACT

A method for encoding image signal, according to the present invention, can: encode a partial block coefficient flag indicating whether a coefficient of a current partial block is a non-zero coefficient; encode a first flag indicating whether an absolute value of the coefficient is greater than 1, encode a second flag indicating whether the absolute value of the coefficient is greater than 2; encode the residual coefficients, which have not been encoded, on the basis of the first flag or the second flag in the current partial block; and encode a code for the coefficient of the current partial block.

This application is a divisional application of U.S. patent applicationSer. No. 16/860,112, filed on Apr. 28, 2020, which is a divisionalapplication of U.S. patent application Ser. No. 16/097,464 filed on Oct.29, 2018, which is a U.S. National Stage Application of InternationalApplication No. PCT/KR2017/004465, filed on Apr. 26, 2017, which claimsthe benefit under 35 USC 119(a) and 365(b) of Korean Patent ApplicationNo. 10-2016-0052691, filed on Apr. 29, 2016, Korean Patent ApplicationNo. 10-2016-0052694, filed on Apr. 29, 2016, Korean Patent ApplicationNo. 10-2016-0052706, filed on Apr. 29, 2016, Korean Patent ApplicationNo. 10-2017-0050048, filed on Apr. 18, 2017, Korean Patent ApplicationNo. 10-2017-0050050, filed on Apr. 18, 2017, Korean Patent ApplicationNo. 10-2017-0050053, filed on Apr. 18, 2017 in the Korean IntellectualProperty Office.

TECHNICAL FIELD

The present invention relates to a method and an apparatus for encodingand decoding image signal.

BACKGROUND ART

Recently, demands for multimedia data such as video have been rapidlyincreasing on internet. However, developing rate of bandwidths ofchannels is hard to follow the amount of multimedia data that is rapidlyincreasing.

DISCLOSURE Technical Problem

An object of the present invention is to improve compression efficiencyof an image by efficiently encoding/decoding coefficients in a partialblock.

An object of the present invention is to improve compression efficiencyof an image by efficiently encoding/decoding partitioning method of atarget encoding/decoding block in encoding/decoding an image.

An object of the present invention is to improve compression efficiencyof an image by efficiently encoding/decoding intra-prediction modeinformation of a target encoding/decoding block in encoding/decoding animage.

Technical Solution

A method and an apparatus for encoding an image signal according to thepresent invention may encode a partial block coefficient flag indicatingwhether a coefficient of a current partial block is a non-zerocoefficient; encode a first flag indicating whether an absolute value ofthe coefficient is greater than 1; encode a second flag indicatingwhether an absolute value of the coefficient is greater than 2; encode aresidual coefficient not encoded based on the first flag or the secondflag in the current partial block; and encode a sign for the coefficientof the current partial block.

A method and an apparatus for encoding an image signal according to thepresent invention may encode a maximum value among absolute values ofcoefficients of the current partial block.

A method and an apparatus for encoding an image signal according to thepresent invention may determine whether absolute values of allcoefficients in the current partial block is smaller than a currentthreshold value; and encoding a first threshold value flag for thecurrent partial block based on a result of the determination.

In a method and an apparatus for encoding an image signal according tothe present invention, when the absolute values of all coefficients inthe current partial block is greater than or equal to the currentthreshold value, the first threshold value flag may be encoded as false,and when the absolute values of all coefficients in the current partialblock is smaller than the current threshold value, the first thresholdvalue flag may be encoded as true.

In a method and an apparatus for encoding an image signal according tothe present invention, when the first threshold value flag is encoded asfalse, the current threshold value may be updated to a next thresholdvalue.

In a method and an apparatus for encoding an image signal according tothe present invention, at least one of the first flag or the second flagmay be selectively encoded according to a value of the first thresholdvalue flag.

In a method and an apparatus for encoding an image signal according tothe present invention, the current threshold value may be a thresholdvalue belonging to a predetermined threshold value range.

In a method and an apparatus for encoding an image signal according tothe present invention, the predetermined threshold value may bedetermined based on at least one of a quantization parameter, a blocksize or a pixel value range.

A method and an apparatus for decoding an image signal according to thepresent invention may decode a partial block coefficient flag indicatingwhether a coefficient of a current partial block is a non-zerocoefficient; decode a first flag indicating whether an absolute value ofthe coefficient is greater than 1; decode a second flag indicatingwhether an absolute value of the coefficient is greater than 2; decode aresidual coefficient not encoded based on the first flag or the secondflag in the current partial block; and decode a sign for the coefficientof the current partial block.

A method and an apparatus for decoding an image signal according to thepresent invention may decode a maximum value among absolute values ofcoefficients of the current partial block.

A method and an apparatus for decoding an image signal according to thepresent invention may decode a first threshold value flag for thecurrent partial block.

In a method and an apparatus for decoding an image signal according tothe present invention, when the first threshold value flag is false,absolute values of all coefficients in the current partial block may begreater than or equal to the current threshold value, and when the firstthreshold flag is true, the absolute values of all coefficients in thecurrent partial block may be smaller than the current threshold value.

In a method and an apparatus for decoding an image signal according tothe present invention, when the first threshold value flag is false, thecurrent threshold value may be updated to a next threshold value.

In a method and an apparatus for decoding an image signal according tothe present invention, at least one of the first flag or the second flagmay be selectively decoded according to a value of the first thresholdvalue flag.

In a method and an apparatus for decoding an image signal according tothe present invention, the current threshold value may be a thresholdvalue belonging to a predetermined threshold value range, and

In a method and an apparatus for decoding an image signal according tothe present invention, the predetermined threshold value may bedetermined based on at least one of a quantization parameter, a blocksize or a pixel value range.

A method and an apparatus for encoding an image signal according to thepresent invention may encode a partial block flag indicating whether atleast one non-zero coefficient exists in a current partial block; encodea partial block coefficient flag indicating whether a currentcoefficient of the current partial block is the non-zero coefficient;encode an absolute value of the current coefficient of the currentpartial block; and encode a sign of the current coefficient of thecurrent partial block.

In a method and an apparatus for encoding an image signal according tothe present invention, the partial block coefficient flag may be encodedbased on the number of non-zero coefficients in a previous partialblock.

In a method and an apparatus for encoding an image signal according tothe present invention, the encoding the partial block coefficient flagmay include changing probability information of the partial blockcoefficient flag based on the number of non-zero coefficients in theprevious partial block.

In a method and an apparatus for encoding an image signal according tothe present invention, the partial block coefficient flag may be encodedbased on the number of non-zero coefficients up to a previouscoefficient in the current partial block.

In a method and an apparatus for encoding an image signal according tothe present invention, the encoding the partial block coefficient flagmay include changing probability information of the partial blockcoefficient flag based on the number of non-zero coefficients up to theprevious coefficient.

A method and an apparatus for decoding an image signal according to thepresent invention may decode a partial block flag indicating whether atleast one non-zero coefficient exists in a current partial block; decodea partial block coefficient flag indicating whether a currentcoefficient of the current partial block is the non-zero coefficient;decode an absolute value of the current coefficient of the currentpartial block; and decode a sign of the current coefficient of thecurrent partial block.

In a method and an apparatus for decoding an image signal according tothe present invention, the partial block coefficient flag may be decodedbased on the number of non-zero coefficients in a previous partialblock.

In a method and an apparatus for decoding an image signal according tothe present invention, the decoding the partial block coefficient flagmay include changing probability information of the partial blockcoefficient flag based on the number of non-zero coefficients in theprevious partial block.

In a method and an apparatus for decoding an image signal according tothe present invention, the partial block coefficient flag may be decodedbased on the number of non-zero coefficients up to a previouscoefficient in the current partial block.

In a method and an apparatus for decoding an image signal according tothe present invention, the decoding the partial block coefficient flagmay include changing probability information of the partial blockcoefficient flag based on the number of non-zero coefficients up to theprevious coefficient.

A method and an apparatus for decoding an image signal according to thepresent invention may decode partitioning information indicating whethera current decoding block is partitioned into two partial blocks, andwhen the partitioning information indicates that the current decodingblock is partitioned into two partial blocks, decode information on apattern of partitioning of the current decoding block, and partition thecurrent decoding block into two partial blocks based on the informationon the pattern of partitioning.

In a method and an apparatus for decoding an image signal according tothe present invention, the information on the pattern of partitioningmay include at least one of direction information indicating apartitioning direction of the current decoding block or information ofdegree of precision that specifies a size of a partial block generatedby partitioning the current decoding block.

In a method and an apparatus for decoding an image signal according tothe present invention, a horizontal length or a vertical length of thepartial block may have a value of dividing the horizontal length or thevertical length of the decoding block by 2 to the power (2^(N)) of avalue (N) specified by the information of degree of precision.

In a method and an apparatus for decoding an image signal according tothe present invention, the information on the pattern of partitioningmay include index information specifying a partitioned shape of thecurrent decoding block.

A method and an apparatus for decoding an image signal according to thepresent invention may determine an MPM (Most Probable Mode) candidatefor a current decoding block based on an intra-prediction mode of aneighboring block neighboring the current decoding block; decodeinformation indicating whether an MPM candidate identical to anintra-prediction mode of the current decoding block exists; and derivethe intra-prediction mode of the current decoding block based on theinformation.

In a method and an apparatus for decoding an image signal according tothe present invention, the number of intra-prediction modes availablefor the current decoding block may be variably determined depending on asize of the current decoding block, a shape of the current decodingblock or an intra-prediction mode of the neighboring block.

In a method and an apparatus for decoding an image signal according tothe present invention, when the number of intra-prediction modesavailable for the current decoding block is different from the number ofintra-prediction modes available for the neighboring block, an MPMcandidate corresponding to a directional prediction mode may be set as aprediction angle of the directional prediction mode.

A method and an apparatus for encoding an image signal according to thepresent invention may determine whether a current encoding block ispartitioned into two partial blocks; encode partitioning informationindicating whether the current encoding block is partitioned into twopartial blocks according to a result of the determination; when thecurrent encoding block is determined to be partitioned into two partialblocks, determine a pattern of partitioning of the current encodingblock; and encode information for the pattern of partitioning of thecurrent encoding block based on the determination.

In a method and an apparatus for encoding an image signal according tothe present invention, the information on the pattern of partitioningmay include at least one of direction information indicating apartitioning direction of the current encoding block or information ofdegree of precision that specifies a size of a partial block generatedby partitioning the current encoding block.

In a method and an apparatus for encoding an image signal according tothe present invention, a horizontal length or a vertical length of thepartial block may have a value of dividing the horizontal length or thevertical length of the encoding block by 2 to the power (2^(N)) of avalue (N) specified by the information of degree of precision.

In a method and an apparatus for encoding an image signal according tothe present invention, the information on the pattern of partitioningmay include index information specifying a partitioned shape of thecurrent encoding block.

A method and an apparatus for encoding an image signal according to thepresent invention may determine an MPM (Most Probable Mode) candidatefor a current encoding block based on an intra-prediction mode of aneighboring block neighboring the current encoding block; determine anintra-prediction mode of the current encoding block; encode informationindicating whether an MPM candidate identical to the intra-predictionmode of the current encoding block exists.

In a method and an apparatus for encoding an image signal according tothe present invention, the number of intra-prediction modes availablefor the current encoding block may be variably determined depending on asize of the current encoding block, a shape of the current encodingblock or an intra-prediction mode of the neighboring block.

In a method and an apparatus for encoding an image signal according tothe present invention, when the number of intra-prediction modesavailable for the current encoding block is different from the number ofintra-prediction modes available for the neighboring block, an MPMcandidate corresponding to a directional prediction mode may be set as aprediction angle of the directional prediction mode.

Advantageous Effects

According to the present invention, compression efficiency of an imagemay be improved by efficiently encoding/decoding coefficients in apartial block.

According to the present invention, compression efficiency of an imagemay be improved by efficiently encoding/decoding partitioning method ofa target encoding/decoding block in encoding/decoding an image.

According to the present invention, compression efficiency of an imagemay be improved by efficiently encoding/decoding intra-prediction modeinformation of a target encoding/decoding block in encoding/decoding animage.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a device for encoding imageaccording to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a device for decoding an imageaccording to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a method for encoding coefficients of atransform block as an embodiment to which the present invention isapplied.

FIG. 4 is a diagram illustrating a method of encoding a maximum value ofa coefficient of a partial block as an embodiment to which the presentinvention is applied.

FIG. 5 is a diagram illustrating a method of encoding a first thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

FIG. 6 is a diagram illustrating a method of encoding a second thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

FIG. 7 is a diagram illustrating a method of decoding coefficients of atransform block as an embodiment to which the present invention isapplied.

FIG. 8 is a diagram illustrating a method of decoding a maximum value ofa coefficient of a partial block as an embodiment to which the presentinvention is applied.

FIG. 9 is a diagram illustrating a method of decoding a first thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

FIG. 10 is a diagram illustrating a method of decoding a secondthreshold value flag for a partial block as an embodiment to which thepresent invention is applied.

FIG. 11 is a diagram illustrating a method of deriving a first/secondthreshold value flag for a current partial block as an embodiment towhich the present invention is applied.

FIG. 12 is a diagram illustrating a method of encoding coefficients of atransform block as an embodiment to which the present invention isapplied.

FIG. 13 is a diagram illustrating a method of encoding a first thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

FIG. 14 is a diagram illustrating a method of decoding coefficients of atransform block as an embodiment to which the present invention isapplied.

FIG. 15 is a diagram illustrating a method of decoding a first thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

FIG. 16 is a diagram illustrating a method of deriving a first thresholdvalue flag for a current partial block as an embodiment to which thepresent invention is applied.

FIG. 17 is a diagram illustrating a method of determining a size/shapeof a partial block based on partitioning index information as anembodiment to which the present invention is applied.

FIG. 18 is a diagram illustrating a method of encoding a partial blockcoefficient flag based on the number of non-zero coefficients in apartial block as an embodiment to which the present invention isapplied.

FIG. 19 is a diagram illustrating a method of changing probabilityinformation of a partial block coefficient flag based on the number ofnon-zero coefficients in a partial block as an embodiment to which thepresent invention is applied.

FIG. 20 is a diagram illustrating a method of encoding a partial blockcoefficient flag based on the number of non-zero coefficients up to acurrent coefficient as an embodiment to which the present invention isapplied.

FIG. 21 is a diagram illustrating a method of changing probabilityinformation of a partial block coefficient flag based on the number ofnon-zero coefficients up to a current coefficient as an embodiment towhich the present invention is applied.

FIG. 22 is a diagram illustrating a method of changing probabilityinformation of a partial block coefficient flag based on the number ofnon-zero coefficients in a partial block as an embodiment to which thepresent invention is applied.

FIG. 23 is a diagram illustrating a method of changing probabilityinformation of a partial block coefficient flag based on the number ofnon-zero coefficients up to a current coefficient as an embodiment towhich the present invention is applied.

FIG. 24 is a block diagram illustrating an image encoding deviceaccording to an embodiment of the present invention.

FIG. 25 is a block diagram illustrating an image decoding deviceaccording to an embodiment of the present invention.

FIG. 26 is a diagram for explaining an intra-prediction method using aDC mode.

FIG. 27 is a diagram for explaining an intra-prediction method using aplanar mode.

FIG. 28 is a diagram for explaining an intra-prediction method using adirectional prediction mode.

FIG. 29 is a diagram illustrating a method of encoding QT partitioninginformation for an encoding block.

FIG. 30 is a diagram illustrating a method of encoding BT partitioninginformation for an encoding block.

FIG. 31 is a diagram illustrating a method of decoding QT partitioninginformation for a decoding block.

FIG. 32 is a diagram illustrating a method of decoding BT partitioninginformation for a decoding block.

FIG. 33 is a diagram illustrating a state of partitioning in an encodingblock.

FIG. 34 is a diagram illustrating an optimal partitioning state of aninput encoding block shown in FIG. 33 using a tree structure.

FIG. 35 is a flowchart illustrating a procedure of controlling thenumber or type of prediction modes in an encoding device.

FIG. 36 and FIG. 37 are diagrams illustrating examples in which 13directional prediction modes are available for the current encodingblock.

FIG. 38 and FIG. 39 are diagrams illustrating examples in which thereare 21 directional prediction modes available for the current block.

FIG. 40 is a flowchart illustrating a procedure of encoding an optimalintra-prediction mode for a current encoding block.

FIG. 41 is a diagram illustrating an example of setting an MPMcandidate.

FIG. 42 and FIG. 43 are diagrams illustrating examples of quantizing aprediction angle.

FIG. 44 is a diagram illustrating another example of setting an MPMcandidate.

FIG. 45 is a diagram illustrating an example of neighboring blocks usedto derive an MPM candidate of a current encoding block.

FIG. 46 is a diagram illustrating an example of deriving an MPMcandidate from a neighboring block that is not adjacent to a currentencoding block.

FIG. 47 is a flowchart illustrating a procedure of decoding anintra-prediction mode for a current decoding block.

BEST MODE

A method and an apparatus for encoding an image signal according to thepresent invention may encode a partial block coefficient flag indicatingwhether a coefficient of a current partial block is a non-zerocoefficient; encode a first flag indicating whether an absolute value ofthe coefficient is greater than 1; encode a second flag indicatingwhether an absolute value of the coefficient is greater than 2; encode aresidual coefficient not encoded based on the first flag or the secondflag in the current partial block; and encode a sign for the coefficientof the current partial block.

A method and an apparatus for encoding an image signal according to thepresent invention may encode a maximum value among absolute values ofcoefficients of the current partial block.

A method and an apparatus for encoding an image signal according to thepresent invention may determine whether absolute values of allcoefficients in the current partial block is smaller than a currentthreshold value; and encoding a first threshold value flag for thecurrent partial block based on a result of the determination.

In a method and an apparatus for encoding an image signal according tothe present invention, when the absolute values of all coefficients inthe current partial block is greater than or equal to the currentthreshold value, the first threshold value flag may be encoded as false,and when the absolute values of all coefficients in the current partialblock is smaller than the current threshold value, the first thresholdvalue flag may be encoded as true.

In a method and an apparatus for encoding an image signal according tothe present invention, when the first threshold value flag is encoded asfalse, the current threshold value may be updated to a next thresholdvalue.

In a method and an apparatus for encoding an image signal according tothe present invention, at least one of the first flag or the second flagmay be selectively encoded according to a value of the first thresholdvalue flag.

In a method and an apparatus for encoding an image signal according tothe present invention, the current threshold value may be a thresholdvalue belonging to a predetermined threshold value range.

In a method and an apparatus for encoding an image signal according tothe present invention, the predetermined threshold value may bedetermined based on at least one of a quantization parameter, a blocksize or a pixel value range.

A method and an apparatus for decoding an image signal according to thepresent invention may decode a partial block coefficient flag indicatingwhether a coefficient of a current partial block is a non-zerocoefficient; decode a first flag indicating whether an absolute value ofthe coefficient is greater than 1; decode a second flag indicatingwhether an absolute value of the coefficient is greater than 2; decode aresidual coefficient not encoded based on the first flag or the secondflag in the current partial block; and decode a sign for the coefficientof the current partial block.

A method and an apparatus for decoding an image signal according to thepresent invention may decode a maximum value among absolute values ofcoefficients of the current partial block.

A method and an apparatus for decoding an image signal according to thepresent invention may decode a first threshold value flag for thecurrent partial block.

In a method and an apparatus for decoding an image signal according tothe present invention, when the first threshold value flag is false,absolute values of all coefficients in the current partial block may begreater than or equal to the current threshold value, and when the firstthreshold flag is true, the absolute values of all coefficients in thecurrent partial block may be smaller than the current threshold value.

In a method and an apparatus for decoding an image signal according tothe present invention, when the first threshold value flag is false, thecurrent threshold value may be updated to a next threshold value.

In a method and an apparatus for decoding an image signal according tothe present invention, at least one of the first flag or the second flagmay be selectively decoded according to a value of the first thresholdvalue flag.

In a method and an apparatus for decoding an image signal according tothe present invention, the current threshold value may be a thresholdvalue belonging to a predetermined threshold value range, and

In a method and an apparatus for decoding an image signal according tothe present invention, the predetermined threshold value may bedetermined based on at least one of a quantization parameter, a blocksize or a pixel value range.

A method and an apparatus for encoding an image signal according to thepresent invention may encode a partial block flag indicating whether atleast one non-zero coefficient exists in a current partial block; encodea partial block coefficient flag indicating whether a currentcoefficient of the current partial block is the non-zero coefficient;encode an absolute value of the current coefficient of the currentpartial block; and encode a sign of the current coefficient of thecurrent partial block.

In a method and an apparatus for encoding an image signal according tothe present invention, the partial block coefficient flag may be encodedbased on the number of non-zero coefficients in a previous partialblock.

In a method and an apparatus for encoding an image signal according tothe present invention, the encoding the partial block coefficient flagmay include changing probability information of the partial blockcoefficient flag based on the number of non-zero coefficients in theprevious partial block.

In a method and an apparatus for encoding an image signal according tothe present invention, the partial block coefficient flag may be encodedbased on the number of non-zero coefficients up to a previouscoefficient in the current partial block.

In a method and an apparatus for encoding an image signal according tothe present invention, the encoding the partial block coefficient flagmay include changing probability information of the partial blockcoefficient flag based on the number of non-zero coefficients up to theprevious coefficient.

A method and an apparatus for decoding an image signal according to thepresent invention may decode a partial block flag indicating whether atleast one non-zero coefficient exists in a current partial block; decodea partial block coefficient flag indicating whether a currentcoefficient of the current partial block is the non-zero coefficient;decode an absolute value of the current coefficient of the currentpartial block; and decode a sign of the current coefficient of thecurrent partial block.

In a method and an apparatus for decoding an image signal according tothe present invention, the partial block coefficient flag may be decodedbased on the number of non-zero coefficients in a previous partialblock.

In a method and an apparatus for decoding an image signal according tothe present invention, the decoding the partial block coefficient flagmay include changing probability information of the partial blockcoefficient flag based on the number of non-zero coefficients in theprevious partial block.

In a method and an apparatus for decoding an image signal according tothe present invention, the partial block coefficient flag may be decodedbased on the number of non-zero coefficients up to a previouscoefficient in the current partial block.

In a method and an apparatus for decoding an image signal according tothe present invention, the decoding the partial block coefficient flagmay include changing probability information of the partial blockcoefficient flag based on the number of non-zero coefficients up to theprevious coefficient.

A method and an apparatus for decoding an image signal according to thepresent invention may decode partitioning information indicating whethera current decoding block is partitioned into two partial blocks, andwhen the partitioning information indicates that the current decodingblock is partitioned into two partial blocks, decode information on apattern of partitioning of the current decoding block, and partition thecurrent decoding block into two partial blocks based on the informationon the pattern of partitioning.

In a method and an apparatus for decoding an image signal according tothe present invention, the information on the pattern of partitioningmay include at least one of direction information indicating apartitioning direction of the current decoding block or information ofdegree of precision that specifies a size of a partial block generatedby partitioning the current decoding block.

In a method and an apparatus for decoding an image signal according tothe present invention, a horizontal length or a vertical length of thepartial block may have a value of dividing the horizontal length or thevertical length of the decoding block by 2 to the power (2^(N)) of avalue (N) specified by the information of degree of precision.

In a method and an apparatus for decoding an image signal according tothe present invention, the information on the pattern of partitioningmay include index information specifying a partitioned shape of thecurrent decoding block.

A method and an apparatus for decoding an image signal according to thepresent invention may determine an MPM (Most Probable Mode) candidatefor a current decoding block based on an intra-prediction mode of aneighboring block neighboring the current decoding block; decodeinformation indicating whether an MPM candidate identical to anintra-prediction mode of the current decoding block exists; and derivethe intra-prediction mode of the current decoding block based on theinformation.

In a method and an apparatus for decoding an image signal according tothe present invention, the number of intra-prediction modes availablefor the current decoding block may be variably determined depending on asize of the current decoding block, a shape of the current decodingblock or an intra-prediction mode of the neighboring block.

In a method and an apparatus for decoding an image signal according tothe present invention, when the number of intra-prediction modesavailable for the current decoding block is different from the number ofintra-prediction modes available for the neighboring block, an MPMcandidate corresponding to a directional prediction mode may be set as aprediction angle of the directional prediction mode.

A method and an apparatus for encoding an image signal according to thepresent invention may determine whether a current encoding block ispartitioned into two partial blocks; encode partitioning informationindicating whether the current encoding block is partitioned into twopartial blocks according to a result of the determination; when thecurrent encoding block is determined to be partitioned into two partialblocks, determine a pattern of partitioning of the current encodingblock; and encode information for the pattern of partitioning of thecurrent encoding block based on the determination.

In a method and an apparatus for encoding an image signal according tothe present invention, the information on the pattern of partitioningmay include at least one of direction information indicating apartitioning direction of the current encoding block or information ofdegree of precision that specifies a size of a partial block generatedby partitioning the current encoding block.

In a method and an apparatus for encoding an image signal according tothe present invention, a horizontal length or a vertical length of thepartial block may have a value of dividing the horizontal length or thevertical length of the encoding block by 2 to the power (2^(N)) of avalue (N) specified by the information of degree of precision.

In a method and an apparatus for encoding an image signal according tothe present invention, the information on the pattern of partitioningmay include index information specifying a partitioned shape of thecurrent encoding block.

A method and an apparatus for encoding an image signal according to thepresent invention may determine an MPM (Most Probable Mode) candidatefor a current encoding block based on an intra-prediction mode of aneighboring block neighboring the current encoding block; determine anintra-prediction mode of the current encoding block; encode informationindicating whether an MPM candidate identical to the intra-predictionmode of the current encoding block exists.

In a method and an apparatus for encoding an image signal according tothe present invention, the number of intra-prediction modes availablefor the current encoding block may be variably determined depending on asize of the current encoding block, a shape of the current encodingblock or an intra-prediction mode of the neighboring block.

In a method and an apparatus for encoding an image signal according tothe present invention, when the number of intra-prediction modesavailable for the current encoding block is different from the number ofintra-prediction modes available for the neighboring block, an MPMcandidate corresponding to a directional prediction mode may be set as aprediction angle of the directional prediction mode.

MODE FOR INVENTION

A variety of modifications may be made to the present invention andthere are various embodiments of the present invention, examples ofwhich will now be provided with reference to drawings and described indetail. However, the present invention is not limited thereto, and theexemplary embodiments can be construed as including all modifications,equivalents, or substitutes in a technical concept and a technical scopeof the present invention. The similar reference numerals refer to thesimilar element in described the drawings.

Terms used in the specification, ‘first’, ‘second’, etc. can be used todescribe various components, but the components are not to be construedas being limited to the terms. The terms are only used to differentiateone component from other components. For example, the ‘first’ componentmay be named the ‘second’ component without departing from the scope ofthe present invention, and the ‘second’ component may also be similarlynamed the ‘first’ component. The term ‘and/or’ includes a combination ofa plurality of items or any one of a plurality of terms.

It will be understood that when an element is simply referred to asbeing ‘connected to’ or ‘coupled to’ another element without being‘directly connected to’ or ‘directly coupled to’ another element in thepresent description, it may be ‘directly connected to’ or ‘directlycoupled to’ another element or be connected to or coupled to anotherelement, having the other element intervening therebetween. In contrast,it should be understood that when an element is referred to as being“directly coupled” or “directly connected” to another element, there areno intervening elements present.

The terms used in the present specification are merely used to describeparticular embodiments, and are not intended to limit the presentinvention. An expression used in the singular encompasses the expressionof the plural, unless it has a clearly different meaning in the context.In the present specification, it is to be understood that terms such as“including”, “having”, etc. are intended to indicate the existence ofthe features, numbers, steps, actions, elements, parts, or combinationsthereof disclosed in the specification, and are not intended to precludethe possibility that one or more other features, numbers, steps,actions, elements, parts, or combinations thereof may exist or may beadded.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.Hereinafter, the same constituent elements in the drawings are denotedby the same reference numerals, and a repeated description of the sameelements will be omitted.

FIG. 1 is a block diagram illustrating a device for encoding imageaccording to an embodiment of the present invention.

Referring to 1, an image encoding device 100 may include a picturepartitioning module 110, prediction modules 120 and 125, a transformmodule 130, a quantization module 135, a rearrangement module 160, anentropy encoding module 165, an inverse quantization module 140, aninverse transform module 145, a filter module 150, and a memory 155.

The constitutional parts shown in FIG. 1 are independently shown so asto represent characteristic functions different from each other in theimage encoding device, and it does not mean that each constitutionalpart is constituted in a constitutional unit of separated hardware orsoftware. In other words, each constitutional part includes each ofenumerated constitutional parts for convenience, and at least twoconstitutional parts of each constitutional part may be combined to formone constitutional part or one constitutional part may be divided into aplurality of constitutional parts to perform each function. Theembodiment where each constitutional part is combined and the embodimentwhere one constitutional part is divided are also included in the scopeof the present invention, if not departing from the essence of thepresent invention.

Also, some of constituents may not be indispensable constituentsperforming essential functions of the present invention but be optionalconstituents improving only performance thereof. The present inventionmay be implemented by including only the indispensable constitutionalparts for implementing the essence of the present invention except theconstituents used in improving performance. The structure including onlythe indispensable constituents except the optional constituents used inimproving only performance is also included in the scope of the presentinvention.

The picture partitioning module 110 may partition an input picture intoat least one block. Here, a block may mean a coding unit (CU), aprediction unit (PU), or a transform unit (TU). The partitioning may beperformed based on at least one of a quad tree or a binary tree. A quadtree is a method of partitioning an upper-level block into fourlower-level blocks whose width and height are half of the upper-levelblock. A binary tree is a method of partitioning an upper-level blockinto two lower-level blocks whose width or height is half of theupper-level block. Using the binary tree-based partitioning, a block mayhave a square shape as well as a non-square shape.

Hereinafter, in embodiments of the present invention, a coding unit maybe used as a unit for performing encoding, or may be used as a unit forperforming decoding.

The prediction modules 120 and 125 may include an inter-predictionmodule 120 for performing inter-prediction and an intra-predictionmodule 125 for performing intra-prediction. Whether to performinter-prediction or intra-prediction for a prediction unit may bedetermined, and specific information (e.g., intra-prediction mode,motion vector, reference picture, etc.) according to each predictionmethod may be determined. Here, a processing unit subjected toprediction may be different from a processing unit for which aprediction method and specific contents are determined. For example, aprediction method, a prediction mode and the like may be determined inunits of prediction unit, and a prediction may be performed in units oftransform unit.

A residual value (residual block) between the generated prediction blockand an original block may be input to the transform module 130. Also,prediction mode information, motion vector information and the like usedfor prediction may be encoded with the residual value by the entropyencoding module 165 and may be transmitted to a decoding device. When aparticular encoding mode is used, it is possible to transmit to adecoding device by encoding the original block as it is withoutgenerating the prediction block through the prediction modules 120 and125.

The inter-prediction module 120 may predict the prediction unit based oninformation of at least one of a previous picture or a subsequentpicture of the current picture, or may predict the prediction unit basedon information of some encoded regions in the current picture, in somecases. The inter-prediction module 120 may include a reference pictureinterpolation module, a motion prediction module, and a motioncompensation module.

The reference picture interpolation module may receive reference pictureinformation from the memory 155 and may generate pixel information of aninteger pixel or less than the integer pixel from the reference picture.In the case of luma pixels, an 8-tap DCT-based interpolation filterhaving different filter coefficients may be used to generate pixelinformation of an integer pixel or less than an integer pixel in unitsof a ¼ pixel. In the case of chroma signals, a 4-tap DCT-basedinterpolation filter having different filter coefficient may be used togenerate pixel information of an integer pixel or less than an integerpixel in units of a ⅛ pixel.

The motion prediction module may perform motion prediction based on areference picture interpolated by the reference picture interpolationmodule. As methods for calculating a motion vector, various methods,such as a full search-based block matching algorithm (FBMA), a threestep search (TSS), a new three-step search algorithm (NTS), etc., may beused. The motion vector may have a motion vector value in units of a ½pixel or a ¼ pixel based on an interpolated pixel. The motion predictionmodule may predict a current prediction unit by changing the motionprediction method. As motion prediction methods, various methods, suchas a skip method, a merge method, an Advanced Motion Vector Prediction(AMVP) method, etc., may be used.

The intra prediction module 125 may generate a prediction unit based onreference pixel information neighboring to a current block which ispixel information in the current picture. When the neighboring block ofthe current prediction unit is a block subjected to inter-prediction andthus a reference pixel is a pixel subjected to inter-prediction, thereference pixel included in the block subjected to inter-prediction maybe replaced with reference pixel information of a neighboring blocksubjected to intra-prediction. That is, when a reference pixel is notavailable, at least one reference pixel of available reference pixelsmay be used instead of unavailable reference pixel information.

Prediction modes in intra-prediction may include a directionalprediction mode using reference pixel information depending on aprediction direction and a non-directional prediction mode not usingdirectional information in performing prediction. A mode for predictingluma information may be different from a mode for predicting chromainformation, and in order to predict the chroma information,intra-prediction mode information used to predict luma information orpredicted luma signal information may be utilized.

In the intra-prediction method, a prediction block may be generatedafter applying an Adaptive Intra Smoothing (AIS) filter to a referencepixel depending on the prediction modes. The type of the AIS filterapplied to the reference pixel may vary. In order to perform the intraprediction method, an intra prediction mode of the current predictionunit may be predicted from the intra prediction mode of the predictionunit neighboring to the current prediction unit. In prediction of theprediction mode of the current prediction unit by using mode informationpredicted from the neighboring prediction unit, when the intraprediction mode of the current prediction unit is the same as the intraprediction mode of the neighboring prediction unit, informationindicating that the prediction modes of the current prediction unit andthe neighboring prediction unit are equal to each other may betransmitted using predetermined flag information, and when theprediction mode of the current prediction unit is different from theprediction mode of the neighboring prediction unit, entropy encoding maybe performed to encode prediction mode information of the current block.

Also, a residual block including information on a residual value whichis a difference between the prediction unit subjected to prediction andthe original block of the prediction unit may be generated based onprediction units generated by the prediction modules 120 and 125. Thegenerated residual block may be input to the transform module 130.

The transform module 130 may transform the residual block includingresidual data using a transform method, such as discrete cosinetransform (DCT), discrete sine transform (DST), and Karhunen LoeveTransform (KLT). Here, a transform method may be determined based onintra-prediction mode of the prediction unit used to generate theresidual block. For example, depending on intra-prediction mode, DCT maybe used for horizontal direction and DST may be used for verticaldirection.

The quantization module 135 may quantize values transformed to afrequency domain by the transform module 130. Quantization coefficientsmay vary depending on the block or importance of a picture. The valuescalculated by the quantization module 135 may be provided to the inversequantization module 140 and the rearrangement module 160.

The transform module unit 130 and/or the quantization module 135 may beselectively included in the image encoding device 100. That is, theimage encoding device 100 may perform at least one of transformation orquantization on the residual data of the residual block, or may skipboth the transformation and the quantization, thereby encoding theresidual block. A block provided as an input of the entropy encodingmodule 165 is generally referred to as a transform block even thougheither the transformation or the quantization is not performed or boththe transformation and the quantization are not performed in the imageencoding device 100.

The rearrangement module 160 may rearrange coefficients of quantizedresidual values.

The rearrangement module 160 may change a coefficient in the form of atwo-dimensional block into a coefficient in the form of aone-dimensional vector through a coefficient scanning method. Forexample, the rearrangement module 160 may scan from a DC coefficient toa coefficient in a high frequency domain using a predetermined scanningmethod so as to change the coefficients to be in the form ofone-dimensional vectors.

The entropy encoding module 165 may perform entropy encoding based onthe values calculated by the rearrangement module 160. Entropy encodingmay use various encoding methods, for example, exponential Golombcoding, context-adaptive variable length coding (CAVLC), andcontext-adaptive binary arithmetic coding (CABAC).

The entropy encoding module 165 may encode various information, such asresidual value coefficient information and block type information of thecoding unit, prediction mode information, partition unit information,prediction unit information and transmit unit information, motion vectorinformation, reference frame information, interpolation information of ablock, filtering information, etc. from the rearrangement module 160 andthe prediction modules 120 and 125. In the entropy encoding module 165,the coefficient of the transform block may be encoded, in units ofpartial block in a transform block, as a non-zero coefficient, acoefficient whose absolute value is larger than 1 or 2, and varioustypes of flags indicating a sign of a coefficient, etc. The coefficientthat is not encoded with only the flag may be encoded through theabsolute value of the difference between the coefficient encoded throughthe flag and the coefficient of the actual transform block. A method ofencoding the coefficients of the transform block will be described indetail with reference to FIG. 3 and FIG. 12.

The entropy encoding module 165 may entropy encode coefficients of thecoding unit input from the rearrangement module 160.

The inverse quantization module 140 may inversely quantize the valuesquantized by the quantization module 135 and the inverse transformmodule 145 may inversely transform the values transformed by thetransform module 130. The residual value generated by the inversequantization module 140 and the inverse transform module 145 may becombined with the prediction unit predicted by a motion estimationmodule, a motion compensation module, and the intra-prediction moduleincluded in the prediction modules 120 and 125 so as to generate areconstructed block.

The filter module 150 may include at least one of a deblocking filter,an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion that occurs due toboundaries between the blocks in the reconstructed picture. In order todetermine whether to perform deblocking, the pixels included in severalrows or columns included in the block may be a basis of determiningwhether to apply the deblocking filter to the current block. When thedeblocking filter is applied to the block, a strong filter or a weakfilter may be applied depending on required deblocking filteringstrength. Also, in applying the deblocking filter, horizontal directionfiltering and vertical direction filtering may be processed in parallel.

The offset correction module may correct offset with the originalpicture in units of a pixel in the picture subjected to deblocking. Inorder to perform the offset correction on a particular picture, it ispossible to use a method of applying offset in consideration of edgeinformation of each pixel or a method of partitioning pixels of apicture into the predetermined number of regions, determining a regionto be subjected to perform offset, and applying the offset to thedetermined region.

Adaptive loop filtering (ALF) may be performed based on the valueobtained by comparing the filtered reconstructed picture and theoriginal picture. The pixels included in the picture may be divided intopredetermined groups, a filter to be applied to each of the groups maybe determined, and filtering may be individually performed for eachgroup. Information on whether to apply ALF and a luma signal may betransmitted by coding units (CU), and the shape and filter coefficientof a filter for ALF may vary depending on each block. Also, the filterfor ALF in the same shape (fixed shape) may be applied regardless ofcharacteristics of the application target block.

The memory 155 may store the reconstructed block or picture calculatedthrough the filter module 150, and the stored reconstructed block orpicture may be provided to the prediction modules 120 and 125 inperforming inter-prediction.

FIG. 2 is a block diagram illustrating a device for decoding an imageaccording to an embodiment of the present invention.

Referring to FIG. 2, the image decoding device 200 may include anentropy decoding module 210, a rearrangement module 215, an inversequantization module 220, an inverse transform module 225, predictionmodules 230 and 235, a filter module 240, and a memory 245.

When an image bitstream is input from the image encoding device, theinput bitstream may be decoded according to an inverse process of theimage encoding device.

The entropy decoding module 210 may perform entropy decoding accordingto an inverse process of entropy encoding by the entropy encoding moduleof the image encoding device. For example, corresponding to the methodsperformed by the image encoding device, various methods, such asexponential Golomb coding, context-adaptive variable length coding(CAVLC), and context-adaptive binary arithmetic coding (CABAC) may beapplied. In the entropy decoding module 210, the coefficient of thetransform block may be decoded, in units of partial block in a transformblock, based on a non-zero coefficient, a coefficient whose absolutevalue is larger than 1 or 2, and various types of flags indicating asign of a coefficient, etc. The coefficient that is not represented byonly the flag may be decoded through combination of coefficientrepresented by the flag and coefficient that is signaled. A method ofdecoding the coefficients of the transform block will be described indetail with reference to FIG. 7 and FIG. 14.

The entropy decoding module 210 may decode information onintra-prediction and inter-prediction performed by the image encodingdevice.

The rearrangement module 215 may perform rearrangement on the bitstreamentropy decoded by the entropy decoding module 210 based on therearrangement method used in the image encoding device. Therearrangement may include reconstructing and rearranging thecoefficients in the form of one-dimensional vectors to the coefficientin the form of two-dimensional blocks. The rearrangement module 215 mayreceive information related to coefficient scanning performed in theimage encoding device and may perform rearrangement via a method ofinversely scanning the coefficients based on the scanning orderperformed in the image encoding device.

The inverse quantization module 220 may perform inverse quantizationbased on a quantization parameter received from the image encodingdevice and the rearranged coefficients of the block.

The inverse transform module 225 may perform the inverse transform ofthe inverse quantized transform coefficients according to apredetermined transform method. Here, the transform method may bedetermined based on a prediction method (inter/intra-prediction), asize/shape of a block, information on intra-prediction mode, etc.

The prediction modules 230 and 235 may generate a prediction block basedon information on prediction block generation received from the entropydecoding module 210 and previously decoded block or picture informationreceived from the memory 245.

The prediction modules 230 and 235 may include a prediction unitdetermination module, an inter-prediction module, and anintra-prediction module. The prediction unit determination module mayreceive various information, such as prediction unit information,prediction mode information of an intra-prediction method, informationon motion prediction of an inter-prediction method, etc. from theentropy decoding module 210, may divide a current coding unit intoprediction units, and may determine whether inter-prediction orintra-prediction is performed on the prediction unit. By usinginformation required in inter-prediction of the current prediction unitreceived from the image encoding device, the inter-prediction module 230may perform inter-prediction on the current prediction unit based oninformation of at least one of a previous picture or a subsequentpicture of the current picture including the current prediction unit.Alternatively, inter-prediction may be performed based on information ofsome pre-reconstructed regions in the current picture including thecurrent prediction unit.

In order to perform inter-prediction, it may be determined for thecoding unit which of a skip mode, a merge mode, an AMVP mode, and aninter block copy mode is used as the motion prediction method of theprediction unit included in the coding unit.

The intra-prediction module 235 may generate a prediction block based onpixel information in the current picture. When the prediction unit is aprediction unit subjected to intra-prediction, intra-prediction may beperformed based on intra-prediction mode information of the predictionunit received from the image encoding device. The intra-predictionmodule 235 may include an adaptive intra smoothing (AIS) filter, areference pixel interpolation module, a DC filter. The AIS filterperforms filtering on the reference pixel of the current block, andwhether to apply the filter may be determined depending on theprediction mode of the current prediction unit. AIS filtering may beperformed on the reference pixel of the current block by using theprediction mode of the prediction unit and AIS filter informationreceived from the image encoding device. When the prediction mode of thecurrent block is a mode where AIS filtering is not performed, the AISfilter may not be applied.

When the prediction mode of the prediction unit is a prediction mode inwhich intra-prediction is performed based on the pixel value obtained byinterpolating the reference pixel, the reference pixel interpolationmodule may interpolate the reference pixel to generate the referencepixel of an integer pixel or less than an integer pixel. When theprediction mode of the current prediction unit is a prediction mode inwhich a prediction block is generated without interpolation thereference pixel, the reference pixel may not be interpolated. The DCfilter may generate a prediction block through filtering when theprediction mode of the current block is a DC mode.

The reconstructed block or picture may be provided to the filter module240. The filter module 240 may include the deblocking filter, the offsetcorrection module, the ALF.

Information on whether or not the deblocking filter is applied to thecorresponding block or picture and information on which of a strongfilter and a weak filter is applied when the deblocking filter isapplied may be received from the image encoding device. The deblockingfilter of the image decoding device may receive information on thedeblocking filter from the image encoding device, and may performdeblocking filtering on the corresponding block.

The offset correction module may perform offset correction on thereconstructed picture based on the type of offset correction and offsetvalue information applied to a picture in performing encoding.

The ALF may be applied to the coding unit based on information onwhether to apply the ALF, ALF coefficient information, etc. receivedfrom the image encoding device. The ALF information may be provided asbeing included in a particular parameter set.

The memory 245 may store the reconstructed picture or block for use as areference picture or block, and may provide the reconstructed picture toan output module.

FIG. 3 is a diagram illustrating a method for encoding coefficients of atransform block as an embodiment to which the present invention isapplied.

A coefficient of a transform block may be encoded in units of apredetermined block (hereinafter, referred to as a partial block) in animage encoding device. A transform block may include one or more partialblocks. A partial block may be a block of N×M size. Here, N and M arenatural numbers, and N and M may be equal to or different from eachother. That is, a partial block may be a square or a non-square block. Asize/shape of a partial block may be fixed (e.g., 4×4) predefined in animage encoding device, or may be variably determined depending on asize/shape of a transform block. Alternatively, an image encoding devicemay determine an optimal size/shape of a partial block in considerationof an encoding efficiency, and encode the partial block. Information ona size/shape of an encoded partial block may be signaled in a level ofat least one of a sequence, a picture, a slice or a block.

An order of encoding partial blocks included in a transform block may bedetermined according to a predetermined scan type (hereinafter, referredto as a first scan type) in an image encoding device. In addition, anorder of encoding coefficients included in a partial block may bedetermined according to a predetermined scan type (hereinafter, referredto as a second scan type). The first scan type and the second scan typemay be the same or different. For the first/second scan type, a diagonalscan, a vertical scan, or a horizontal scan and the like may be used.However, the present invention is not limited thereto, and one or morescan types having predetermined angles may be further added. Thefirst/second scan type may be determined based on at least one of codingblock related information (e.g., maximum/minimum size, partitioningtechnique, etc.), size/shape of transform block, size/shape of partialblock, prediction mode, intra-prediction related information (e.g., avalue of intra-prediction mode, directionality, angle, etc.) orinter-prediction related information.

An image encoding device may encode, in a transform block, positioninformation of a coefficient (hereinafter, referred to as a non-zerocoefficient) having non-zero value first appeared in the above-describedencoding order. Encoding may be performed sequentially from a partialblock including the non-zero coefficient. Hereinafter, referring to FIG.3, a procedure of encoding coefficients of a partial block will bedescribed.

A partial block flag for a current partial block may be encoded (S300).The partial block flag may be encoded in units of a partial block. Thepartial block flag may indicate whether there is at least one non-zerocoefficient in the current partial block. For example, when the partialblock flag is a first value, it may indicate that the current partialblock includes at least one non-zero coefficient, and when the partialblock flag is a second value, it may indicate that all coefficients ofthe current partial block are 0.

A partial block coefficient flag for a current partial block may beencoded (S310). The partial block coefficient flag may be encoded inunits of a coefficient. The partial block coefficient flag may indicatewhether a coefficient is a non-zero coefficient. For example, when thecoefficient is a non-zero coefficient, the partial block coefficientflag may be encoded to a first value, and when the coefficient is zero,the partial block coefficient flag may be encoded to a second value. Thepartial block coefficient flag may be selectively encoded according tothe partial block flag. For example, a current partial block may beencoded for each coefficient of a partial block only when there is atleast one non-zero coefficient present in the current partial block(i.e., the partial block flag is a first value).

A flag (hereinafter, referred to as a first flag) indicating whether anabsolute value of a coefficient is greater than 1 may be encoded (S320).The first flag may be selectively encoded according to a value of thepartial block coefficient flag. For example, when the coefficient is anon-zero coefficient (i.e., the partial block coefficient flag is afirst value), the first flag may be encoded by checking whether anabsolute value of the coefficient is greater than 1. When the absolutevalue of the coefficient is greater than 1, the first flag is encoded toa first value, and when the absolute value of the coefficient is notgreater than 1, the first flag may be encoded to a second value.

A flag (hereinafter, referred to as a second flag) indicating whether anabsolute value of a coefficient is greater than 2 may be encoded (S330).The second flag may be selectively encoded according to a value of thefirst flag. For example, when the coefficient is greater than 1 (i.e.,the first flag is a first value), the second flag may be encoded bychecking whether an absolute value of the coefficient is greater than 2.When the absolute value of the coefficient is greater than 2, the secondflag is encoded to a first value, and when the absolute value of thecoefficient is not greater than 2, the second flag may be encoded to asecond value.

The number of at least one of the first flag or the second flag may beat least one to at most N*M. Alternatively, at least one of the firstflag or the second flag may be a fixed number (e.g., one, two, or more)predefined in an image encoding device. The number of the first/secondflag may be different depending on a bit depth of an input image, adynamic range of an original pixel value in a certain region of animage, a block size/depth, a partitioning technique (e.g., quad tree,binary tree), a transforming technique (e.g., DCT, DST), whether to skiptransform, quantization parameters, prediction mode (e.g., intra/intermode), and so on. In addition to the first/second flag, an n-th flagindicating whether an absolute value of a coefficient is greater than nmay be additionally encoded. Here, n may mean a natural number greaterthan two. The number of the n-th flag may be one, two, or more, and maybe determined in the same/similar manner as the first/second flagdescribed above.

Remaining coefficients that are not encoded based on the first/secondflag may be encoded in a current partial block (S340). Here, theencoding may be a procedure of encoding the coefficient value itself.The remaining coefficients may be equal to or greater than two.

A sign for a coefficient of a partial block may be encoded (S350). Thesign may be encoded in a flag format in units of a coefficient. The signmay be selectively encoded according to a value of the partial blockcoefficient flag described above. For example, the sign may be encodedonly when the coefficient is a non-zero coefficient (i.e., the partialblock coefficient flag is a first value).

In addition, above-described encoding coefficients of a partial blockmay further include a procedure of specifying a range of coefficientvalues belonging to the partial block. Through the above procedure, itmay be confirmed whether or not at least one non-zero coefficient existsin a partial block. The above procedure may be implemented through atleast one of (A) encoding a maximum value, (B) encoding a firstthreshold value flag or (C) encoding a second threshold value flag whichwill be described below. The above procedure may be implemented by beingincluded in any one of the above-described steps S300 to S350, or may beimplemented in a form that is substituted for at least one of steps S300to S350. Hereinafter, the procedure of specifying a range of coefficientvalues belonging to a partial block will be described in detail withreference to FIG. 4 to FIG. 6.

FIG. 4 is a diagram illustrating a method of encoding a maximum value ofa coefficient of a partial block as an embodiment to which the presentinvention is applied.

Referring to FIG. 4, a maximum value among an absolute values ofcoefficients of a current partial block may be encoded (S400). Throughthe maximum value, a range of coefficient values belonging to thecurrent partial block may be inferred. For example, when the maximumvalue is m, coefficients of the current partial block may fall withinthe range of 0 to m. The maximum value may be selectively encodedaccording to a value of the partial block flag described above. Forexample, the maximum value may be encoded only when a current partialblock includes at least one non-zero coefficient (i.e., the partialblock flag is a first value). When coefficients of the current partialblock are all 0 (i.e., the partial block flag is a second value), themaximum value may be derived as 0.

In addition, through the maximum value, it may be determined whether ornot at least one non-zero coefficient is included in a current partialblock. For example, when the maximum value is greater than 0, thecurrent partial block includes at least one non-zero coefficient, andwhen the maximum value is 0, all coefficients of the current partialblock may be 0. Therefore, encoding the maximum value may be performedin place of the encoding of the partial block flag of S300.

FIG. 5 is a diagram illustrating a method of encoding a first thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

A first threshold value flag of the present invention may indicatewhether or not all coefficients of a partial block are smaller than apredetermined threshold value. The number of threshold values may be N(N>=1), where a range of threshold values may be represented by {T₀, T₁,T₂, . . . , T_(N-1)}. Here, the 0th threshold value T₀ denotes a minimumvalue, and the (N−1)-th threshold value T_(N-1) denotes a maximum value,and {T₀, T₁, T₂, . . . , T_(N-1)} may be those in which the thresholdvalues are arranged in ascending order. The number of the thresholdvalues may be predetermined in an image encoding device. The imageencoding device may determine an optimal number of threshold values inconsideration of encoding efficiency and encode the number.

The threshold value may be obtained by setting the minimum value to 1and increasing the minimum value by n (n>=1). The threshold value may bepredetermined in an image encoding device. The image encoding device maydetermine an optimal threshold value in consideration of the encodingefficiency and encode the threshold value.

The range of the threshold value may be determined differently dependingon a quantization parameter (QP). The QP may be set at a level of atleast one of a sequence, a picture, a slice, or a transform block.

For example, when the QP is greater than a predetermined QP threshold,it may be expected that the distribution of zero coefficients in atransform block will be higher. In this case, the range of the thresholdvalue may be determined as {3}, or the encoding procedure of thefirst/second threshold value flag may be omitted, and coefficients of apartial block may be encoded through steps S300 to S350 described above.

When the QP is smaller than a predetermined QP threshold, it may beexpected that the distribution of non-zero coefficients in a transformblock will be higher. In this case, the range of the threshold value maybe determined as {3, 5} or {5, 3}.

That is, the range of threshold values when QP is small may have thenumber and/or size (e.g., maximum value) of the threshold valuesdifferent from the threshold value range when QP is large. The number ofQP threshold values may be one, two, or more. The QP threshold value maybe predetermined in an image encoding device. For example, the QPthreshold value may correspond to a median value of a range of QPsavailable in the image encoding device. Alternatively, the imageencoding device may determine an optimal QP threshold value consideringencoding efficiency, and encode the QP threshold value.

Alternatively, a range of threshold values may be determined differentlydepending on the size/shape of a block. Here, a block may mean a codingblock, a prediction block, a transform block, or a partial block. Thesize may be represented by at least one of a width, a height, a sum of awidth and a height, or the number of coefficient.

For example, when a size of a block is smaller than a predeterminedthreshold size, a range of threshold values may be determined as {3}, orthe encoding procedure of the first/second threshold value flag may beomitted, and coefficients of a partial block may be encoded throughsteps S300 to S350 described above. When a size of a block is largerthan a predetermined threshold size, a range of threshold values may bedetermined as {3, 5} or {5, 3}.

That is, the range of threshold values when a block size is small mayhave the number and/or size (e.g., maximum value) of the thresholdvalues different from the threshold value range when a block size islarge. The number of threshold size may be one, two, or more. Thethreshold size may be predetermined in an image encoding device. Forexample, the threshold size may be represented by a×b, wherein a and bare 2, 4, 8, 16, 32, 64 or more, and a and b may be equal to ordifferent from each other. Alternatively, the image encoding device maydetermine an optimal threshold size considering encoding efficiency, andencode the threshold size.

Alternatively, the range of threshold values may be determineddifferently depending on a range of pixel values. The range of pixelvalues may be represented by a maximum value and/or a minimum value ofpixels belonging to a predetermined region. Here, the predeterminedregion may mean at least one of a sequence, a picture, a slice, or ablock.

For example, when the difference between the maximum value and theminimum value of the range of pixel values is smaller than apredetermined threshold difference value, the range of threshold valuesis determined as {3}, or the encoding procedure of the first/secondthreshold value flag may be omitted, and coefficients of a partial blockmay be encoded through steps S300 to S350 described above. When thedifference is larger than a predetermined threshold difference value,the range of threshold values may be determined as {3, 5} or {5, 3}.

That is, the range of threshold values when the difference is small mayhave the number and/or size (e.g., maximum value) of the thresholdvalues different from a range of threshold values when the difference islarge. The number of threshold difference values may be one, two, ormore. The threshold difference value may be predetermined in an imageencoding device. Alternatively, the image encoding device may determinean optimal threshold difference value considering encoding efficiency,and encode the threshold difference value.

Referring to FIG. 5, it may be determined whether absolute values of allcoefficients in a current partial block is smaller than a currentthreshold value (S500).

When the absolute values of all coefficients are not smaller than thecurrent threshold value, a first threshold value flag may be encoded as“false” (S510). In this case, the current threshold value (i-ththreshold value) may be updated to the next threshold value ((i+1)-ththreshold value) (S520), and the above described step S500 may beperformed based on the updated current threshold value. Alternatively,when absolute values of all coefficients are not smaller than thecurrent threshold value, the first threshold value flag encodingprocedure of step S510 may be omitted, and the current threshold valuemay be updated to the next threshold value.

When the current threshold value reaches a maximum value of a thresholdvalue or when the number of the threshold values is 1, the currentthreshold value may be updated by adding a predetermined constant to thecurrent threshold value. The predetermined constant may be an integergreater than or equal to one. Here, the update may be repeatedlyperformed until the first threshold value flag is encoded as “true”.Based on the updated current threshold value, step S500 may beperformed. Alternatively, when the current threshold value reaches themaximum value of the threshold value or when the number of thresholdvalues is 1, the updating procedure may be terminated.

When absolute values of all coefficients are smaller than a currentthreshold value, the first threshold value flag may be encoded as “true”(S530).

As described above, when the first threshold value flag for the i-ththreshold value is “true”, this may indicate that absolute values of allcoefficients in a partial block are smaller than the i-th thresholdvalue. When the first threshold value flag for the i-th threshold is“false”, this may indicate that absolute values of all coefficients inthe partial block is greater than or equal to the i-th threshold. Basedon the first threshold flag that is “true”, a range of coefficientvalues belonging to the partial block may be specified. That is, whenthe first threshold value flag for the i-th threshold value is “true”,the coefficient belonging to the partial block may fall within the rangeof 0 to (i-th threshold value−1).

According to the encoded first threshold value flag, at least one ofsteps S300 to S350 described above may be omitted.

For example, when a range of threshold values is {3, 5}, at least one ofthe first threshold value flag for the threshold value “3” or the firstthreshold value flag for the threshold value “5” may be encoded. Whenthe first threshold value flag for the threshold value “3” is “true”,absolute values of all coefficients in the partial block may fall withinthe range of 0 to 2. In this case, coefficients of the partial block maybe encoded by performing the remaining steps except at least one of theabove-described steps S330 or S340, or the coefficients of the partialblock may be encoded by performing the remaining steps except at leastone of S300, S330 or S340.

When the first threshold value flag for the threshold “3” is “false”,the first threshold value flag for the threshold “5” may be encoded.When the first threshold value flag for the threshold “5” is “false”, atleast one of absolute values of coefficients in a partial block may begreater than or equal to 5. In this case, coefficients of the partialblock may be encoded by performing the above-described steps S300 toS350 in the same manner, or coefficients of the partial block may beencoded by performing the remaining steps except step S300.

When the first threshold value flag for the threshold “5” is “true”,absolute values of all coefficients in the partial block may fall withinthe range of 0 to 4. In this case, coefficients of the partial block maybe encoded by performing the above-described steps S300 to S350 in thesame manner, or coefficients of the partial block may be encoded byperforming the remaining steps except step S300.

In addition, a first threshold value flag of a current partial block maybe derived based on a first threshold flag of another partial block. Inthis case, the encoding procedure of the first threshold value flag maybe omitted, and this will be described with reference to FIG. 11.

FIG. 6 is a diagram illustrating a method of encoding a second thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

A second threshold flag of the present invention may indicate whether ornot all coefficients of a partial block are smaller than a predeterminedthreshold value. The number of threshold values may be N (N>=1), where arange of threshold values may be represented by {T₀, T₁, T₂, . . . ,T_(N-1)}. Here, T₀, which is the 0th threshold value, is a maximumvalue, and T_(N-1), which is the (N−1)-th threshold value, is a minimumvalue, and {T₀, T₁, T₂, . . . , T_(N-1)} may be those in which thethreshold values are arranged in descending order. The number of thethreshold values may be predetermined in an image encoding device. Theimage encoding device may determine an optimal number of thresholdvalues considering encoding efficiency, and encode the number.

The threshold value may be obtained by setting a maximum value to m anddecreasing the minimum value by n (n>=1). The m may be predetermined inan image encoding device. Alternatively, the image encoding device maydetermine an optimal maximum value m considering encoding efficiency,and encode the maximum value. The threshold value may be predeterminedin the image encoding device. The image encoding device may determinethe optimal threshold value considering encoding efficiency and encodethe threshold value.

A range of threshold values may be determined differently depending onat least one of a quantization parameter, a size/shape of a block, or arange of pixel values, as described in the embodiment of FIG. 5.

Referring to FIG. 6, it may be determined whether absolute values of allcoefficients in a current partial block is smaller than a currentthreshold value (S600).

When absolute values of all coefficients are smaller than the currentthreshold value, the second threshold value flag may be encoded as“true” (S610). In this case, the current threshold value (i-th thresholdvalue) may be updated to the next threshold value ((i+1)-th thresholdvalue) (S620), and the above described step S600 may be performed basedon the updated current threshold value. Alternatively, when the absolutevalues of all coefficients are smaller than the current threshold value,the second threshold value flag encoding process in step S610 may beomitted, and the current threshold value may be updated to the nextthreshold value.

When the current threshold value reaches the minimum value of thethreshold value or when the number of threshold values is 1, the currentthreshold value may be updated by subtracting a predetermined constantfrom the current threshold value. The predetermined constant may be aninteger greater than or equal to 1. Here, the update may be repeatedlyperformed until the second threshold value flag is encoded as “false”.Analogously, based on the updated current threshold value, step S600described above may be performed. Alternatively, when the currentthreshold value reaches the minimum value of the threshold value or whenthe number of threshold values is 1, the updating procedure may beterminated.

When absolute values of all coefficients are not smaller than thecurrent threshold value, the second threshold value flag may be encodedas “false” (S630).

As described above, when the second threshold value flag for the i-ththreshold value is “true”, this may indicate that absolute values of allcoefficients in the partial block is smaller than the i-th thresholdvalue. When the second threshold value flag for the i-th threshold valueis “false”, this may indicate that at least one of the absolute valuesof all coefficients in the partial block is greater than or equal to thei-th threshold value.

According to the encoded second threshold value flag, at least one ofsteps S300 to S350 described above may be omitted.

For example, when a range of threshold values is {5, 3}, at least one ofthe second threshold value flag for the threshold value “5” or thesecond threshold value flag for the threshold value “3” may be encoded.When the second threshold value flag for the threshold value “5” is“false”, at least one of the absolute values of all coefficients in thepartial block may be greater than or equal to 5. In this case,coefficients of the partial block may be encoded by performing theabove-described steps S310 to S350 in the same manner, or coefficientsof the partial block may be encoded by performing the remaining stepsexcept step S300.

When the second threshold value flag for the threshold value “5” is“true”, the second threshold value flag for the threshold value “3” maybe encoded. When the second threshold flag for the threshold value “3”is “true”, the absolute values of coefficients in the partial block mayfall within the range of 0 to 2. In this case, coefficient of thepartial block may be encoded by performing the remaining steps except atleast one of the above-described steps S330 and S340, or coefficients ofthe partial block may be encoded by performing the remaining stepsexcept at least one of S300, S330 or S340.

When the second threshold value flag for the threshold value “3” is“false”, at least one of absolute values of all coefficients in thepartial block may be equal to or greater than 3. In this case,coefficients of the partial block may be encoded by performing theabove-described steps S300 to S350 in the same manner, or coefficientsof the partial block may be encoded by performing the remaining stepsexcept step S300.

In addition, the second threshold value flag of the current partialblock may be derived based on the second threshold value flag of anotherpartial block. In this case, the second threshold value flag encodingprocedure may be omitted, and this will be described with reference toFIG. 11.

FIG. 7 is a diagram illustrating a method of decoding coefficients of atransform block as an embodiment to which the present invention isapplied.

Coefficients of a transform block may be decoded in units of apredetermined block (hereinafter, referred to as a partial block) in animage decoding device. A transform block may include one or more partialblocks. A partial block may be a block of N×M size. Here, N and M arenatural numbers, and N and M may be equal to or different from eachother. That is, a partial block may be a square or a non-square block. Asize/shape of a partial block may be fixed (e.g., 4×4) predefined in animage decoding device, may be variably determined depending on asize/shape of a transform block, or may be variably determined based onsignaled information on a size/shape of a partial block. Information ona size/shape of a partial block may be signaled in a level of at leastone of a sequence, a picture, a slice or a block.

An order of decoding partial blocks belonging to a transform block maybe determined according to a predetermined scan type (hereinafter,referred to as a first scan type) in an image decoding device. Inaddition, an order of decoding coefficients belonging to a partial blockmay be determined according to a predetermined scan type (hereinafter,referred to as a second scan type). The first scan type and the secondscan type may be the same or different. For the first/second scan type,a diagonal scan, a vertical scan, a horizontal scan and the like may beused. However, the present invention is not limited thereto, and one ormore scan types having predetermined angles may be further added. Thefirst/second scan type may be determined based on at least one of codingblock related information (e.g., maximum/minimum size, partitioningtechnique, etc.), size/shape of transform block, size/shape of partialblock, prediction mode, intra-prediction related information (e.g., avalue of intra-prediction mode, directionality, angle, etc.) orinter-prediction related information.

An image decoding device may decode, in a transform block, positioninformation of a coefficient (hereinafter, referred to as a non-zerocoefficient) having non-zero value first appeared in the above-describeddecoding order. Decoding may be performed sequentially from a partialblock according to the position information. Hereinafter, a procedure ofdecoding coefficients of a partial block will be described withreference to FIG. 3.

A partial block flag for a current partial block may be decoded (S700).The partial block flag may be decoded in units of a partial block. Thepartial block flag may indicate whether there is at least one non-zerocoefficient in the current partial block. For example, when the partialblock flag is a first value, it may indicate that the current partialblock includes at least one non-zero coefficient, and when the partialblock flag is a second value, it may indicate that all coefficients ofthe current partial block are 0.

A partial block coefficient flag for a current partial block may bedecoded (S710). The partial block coefficient flag may be decoded inunits of a coefficient. The partial block coefficient flag may indicatewhether the coefficient is a non-zero coefficient. For example, when thepartial block coefficient flag is a first value, it may indicate thatthe coefficient is a non-zero coefficient, and when the partial blockcoefficient flag is a second value, it may indicate that the coefficientis zero. The partial block coefficient flag may be selectively decodedaccording to the partial block flag. For example, a current partialblock may be decoded for each coefficient of a partial block only whenthere is at least one non-zero coefficient present in the currentpartial block (i.e., the partial block flag is a first value).

A flag (hereinafter, referred to as a first flag) indicating whether anabsolute value of a coefficient is greater than 1 may be decoded (S720).The first flag may be selectively decoded according to a value of thepartial block coefficient flag. For example, when the coefficient is anon-zero coefficient (i.e., the partial block coefficient flag is afirst value), the first flag may be decoded to check whether theabsolute value of the coefficient is greater than 1. When the first flagis a first value, the absolute value of the coefficient is greater than1, and when the first flag is a second value, the absolute value of thecoefficient may be 1.

A flag (hereinafter, referred to as a second flag) indicating whether anabsolute value of a coefficient is greater than 2 may be decoded (S730).The second flag may be selectively decoded according to a value of thefirst flag. For example, when the coefficient is greater than 1 (i.e.,the first flag is a first value), the second flag may be decoded tocheck whether the absolute value of the coefficient is greater than 2.When the second flag is a first value, the absolute value of thecoefficient is greater than 2, and when the second flag is a secondvalue, the absolute value of the coefficient may be 2.

The number of at least one of the first flag or the second flag may beat least one to at most N*M. Alternatively, at least one of the firstflag or the second flag may be a fixed number (e.g., one, two, or more)predefined in an image decoding device. The number of the first/secondflag may be different depending on a bit depth of an input image, adynamic range of an original pixel value in a certain region of animage, a block size/depth, a partitioning technique (e.g., quad tree,binary tree), a transforming technique (e.g., DCT, DST), whether to skiptransform, quantization parameters, prediction mode (e.g., intra/intermode), and so on. In addition to the first/second flag, an n-th flagindicating whether an absolute value of a coefficient is greater than nmay be additionally decoded. Here, n may mean a natural number greaterthan two. The number of the n-th flag may be one, two, or more, and maybe determined in the same/similar manner as the first/second flagdescribed above.

Remaining coefficients that are not decoded based on the first/secondflag may be decoded in a current partial block (S740). Here, thedecoding may be a procedure of decoding the coefficient value itself.The remaining coefficients may be equal to or greater than two.

A sign for a coefficient of a partial block may be decoded (S750). Thesign may be decoded in a flag format in units of a coefficient. The signmay be selectively decoded according to a value of the partial blockcoefficient flag described above. For example, the sign may be decodedonly when the coefficient is a non-zero coefficient (i.e., the partialblock coefficient flag is a first value).

In addition, above-described decoding coefficients of a partial blockmay further include a procedure of specifying a range of coefficientvalues belonging to the partial block. Through the above procedure, itmay be confirmed whether or not at least one non-zero coefficient existsin a partial block. The above procedure may be implemented through atleast one of (A) decoding a maximum value, (B) decoding a firstthreshold value flag or (C) decoding a second threshold value flag whichwill be described below. The above procedure may be implemented by beingincluded in any one of the above-described steps S700 to S750, or may beimplemented in a form that is substituted for at least one of steps S700to S370. Hereinafter, the procedure of specifying a range of coefficientvalues belonging to a partial block will be described in detail withreference to FIG. 8 to FIG. 10.

FIG. 8 is a diagram illustrating a method of decoding a maximum value ofa coefficient of a partial block as an embodiment to which the presentinvention is applied.

Referring to FIG. 8, information indicating a maximum value amongabsolute values of coefficients of a current partial block may bedecoded (S800). A range of coefficient values belonging to the currentpartial block may be inferred through the maximum value according to theinformation. For example, when the maximum value is m, coefficients ofthe current partial block may fall within the range of 0 to m. Theinformation indicating the maximum value may be selectively decodedaccording to a value of the partial block flag described above. Forexample, a current partial block may be decoded only when the currentpartial block includes at least one non-zero coefficient (i.e., thepartial block flag is a first value). When coefficients of the currentpartial block are all 0 (i.e., the partial block flag is the secondvalue), the information indicating the maximum value may be derived aszero.

Also, through the maximum value according to the information, it may bedetermined whether or not at least one non-zero coefficient is includedin a current partial block. For example, when the maximum value isgreater than 0, the current partial block includes at least one non-zerocoefficient, and when the maximum value is 0, all coefficients of thecurrent partial block may be zero. Therefore, the decoding the maximumvalue may be performed in place of the decoding of the partial blockflag of S700.

FIG. 9 is a diagram illustrating a method of decoding a first thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

A first threshold flag of the present invention may indicate whether ornot all coefficients of a partial block are smaller than a predeterminedthreshold value. The number of threshold values may be N (N>=1), where arange of threshold values may be represented by {T₀, T₁, T₂, . . . ,T_(N-1)}. Here, the 0th threshold value T₀ may denote a minimum value,and the (N−1)-th threshold value T_(N-1) may denotes a maximum value,and {T₀, T₁, T₂, . . . , T_(N-1)} may be those in which the thresholdvalues are arranged in ascending order. The number of threshold valuesmay be predetermined in an image decoding device or may be determinedbased on signaled information on the number of threshold values.

The threshold value may be obtained by setting a minimum value to 1 andincreasing the minimum value by n (n>=1). The threshold value may be setin an image decoding device or may be determined based on signaledinformation on a threshold value.

A range of threshold values may be determined differently depending on aquantization parameter (QP). The QP may be set at a level of at leastone of a sequence, a picture, a slice, or a transform block.

For example, when the QP is larger than a predetermined QP thresholdvalue, a range of threshold values may be determined as {3}, or thefirst/second threshold value flag decoding procedure may be omitted, andthrough the above-described steps of S700 to S750 coefficients of apartial block may be decoded.

In addition, when the QP is smaller than a predetermined QP threshold, arange of threshold values may be determined as {3, 5} or {5, 3}.

That is, a range of threshold values when the QP is small may have thenumber and/or size (e.g., maximum value) of threshold values differentfrom a range of threshold values when the QP is large. The number of QPthreshold values may be one, two, or more. The QP threshold value may beset in an image decoding device. For example, the QP threshold value maycorrespond to a median value of a range of QPs available in an imagedecoding device. Alternatively, the QP threshold value may be determinedbased on information on the QP threshold value signaled by an imageencoding device.

Alternatively, a range of threshold values may be determined differentlydepending on a size/shape of a block. Here, a block may mean a codingblock, a prediction block, a transform block, or a partial block. Thesize may be represented by at least one of a width, a height, a sum of awidth and a height, or the number of coefficients.

For example, when a block size is smaller than a predetermined thresholdsize, a range of threshold values may be determined as {3}, or thefirst/second threshold value flag decoding procedure may be omitted, andcoefficients of a partial block may be decoded through steps S700 toS750 described above. In addition, when a block size is larger than apredetermined threshold size, a range of threshold values may bedetermined as {3, 5} or {5, 3}.

That is, a range of threshold values when a block size is small may havethe number and/or size (e.g., maximum value) of threshold valuesdifferent from a range of threshold values when a block size is large.The number of threshold size may be one, two, or more. The thresholdsize may be set in an image decoding device. For example, the thresholdsize may be represented by a×b, where a and b are 2, 4, 8, 16, 32, 64 ormore, and a and b may be the same or different. Alternatively, thethreshold size may be determined based on information on a thresholdsize signaled by an image encoding device.

Alternatively, a range of threshold values may be determined differentlydepending on a range of pixel values. The range of pixel values may berepresented by a maximum value and/or a minimum value of pixelsbelonging to a predetermined region. Here, the predetermined region maymean at least one of a sequence, a picture, a slice, or a block.

For example, when a difference between a maximum value and a minimumvalue of a range of pixel values is smaller than a predeterminedthreshold difference value, a range of threshold values may bedetermined as {3}, or the first/second threshold value flag decodingprocedure may be omitted, and coefficients of a partial block may bedecoded through steps S700 to S750 described above. In addition, whenthe difference is larger than a predetermined threshold differencevalue, the range of threshold values may be determined as {3, 5} or {5,3}.

That is, a range of threshold values when the difference is small mayhave the number and/or size (e.g., maximum value) of threshold valuesdifferent from a range of threshold values when the difference is large.The number of threshold difference values may be one, two, or more. Thethreshold difference value may be set in an image decoding device or maybe determined based on information on a threshold difference valuesignaled by an image encoding device.

Referring to FIG. 9, a first threshold value flag for a currentthreshold value may be decoded (S900).

The first threshold value flag may indicate whether absolute values ofall coefficients of a partial block are smaller than a current thresholdvalue. For example, when the first threshold value flag is “false”, itmay indicate that absolute values of all coefficients of a partial blockare greater than or equal to a current threshold. In addition, when thefirst threshold value flag is “true”, it may indicate that absolutevalues of all coefficients of a partial block are smaller than a currentthreshold value.

When the first threshold value flag is “false”, the current thresholdvalue (i-th threshold value) may be updated to the next threshold value((i+1-th threshold value) (S910), based on the updated current thresholdvalue, step S900 described above may be performed.

When the current threshold value reaches a maximum value of thresholdvalues or when the number of threshold values is 1, the currentthreshold value may be updated by adding a predetermined constant to thecurrent threshold value. The predetermined constant may be an integergreater than or equal to one. Here, the update may be repeatedlyperformed until the first threshold value that is “true” is decoded.Alternatively, when the current threshold value reaches a maximum valueof threshold values or when the number of threshold values is 1, theupdating procedure may be terminated.

As shown in FIG. 9, when the first threshold value flag is “true”,decoding of a first threshold value flag may not be performed any more.

As described above, when a first threshold value flag for the i-ththreshold value is “true”, it may indicate that absolute values of allcoefficients in a partial block are smaller than the i-th thresholdvalue. In addition, when a first threshold flag for the i-th thresholdvalue is “false”, it may indicate that absolute values of allcoefficients in a partial block are greater than or equal to the i-ththreshold value. Based on the first threshold value flag that is “true”,a range of coefficient values belonging to a partial block may bespecified. That is, when a first threshold value flag for the i-ththreshold value is “true”, a coefficient belonging to a partial blockmay fall within a range of 0 to (i-th threshold value−1).

According to the decoded first threshold value flag, at least one ofsteps S700 to S750 described above may be omitted.

For example, when a range of threshold values is {3, 5}, at least one ofa first threshold value flag for the threshold value “3” or a firstthreshold value flag for the threshold value “5” may be decoded. Whenthe first threshold value flag for the threshold value “3” is “true”,absolute values of all coefficients in a partial block may fall withinthe range of 0 to 2. In this case, coefficients of a partial block maybe decoded by performing the remaining steps except at least one of thesteps S730 or S740 described above, or coefficients of a partial blockmay be decoded by performing the remaining steps except at least one ofthe steps S700, S730 or S740 described above.

When the first threshold value flag for the threshold value “3” is“false”, the first threshold value flag for the threshold value “5” maybe decoded. When the first threshold value flag for the threshold value“5” is “false”, at least one of absolute values of coefficients in apartial block may be greater than or equal to 5. In this case,coefficients of a partial block may be decoded by performing theabove-described steps S700 to S750 in the same manner, or coefficientsof a partial block may be decoded by performing the remaining stepsexcept step S700.

In addition, when the first threshold value flag for the threshold value“5” is “true”, absolute values of all coefficients in a partial blockmay fall within the range of 0 to 4. In this case, coefficients of apartial block may be decoded by performing the above-described stepsS700 to S750 in the same manner, or coefficients of a partial block maybe decoded by performing the remaining steps except step S700.

In addition, a first threshold value flag of a current partial block maybe derived based on a first threshold value flag of another partialblock. In this case, decoding procedure for a first threshold value flagmay be omitted, and this will be described with reference to FIG. 11.

FIG. 10 is a diagram illustrating a method of decoding a secondthreshold value flag for a partial block as an embodiment to which thepresent invention is applied.

A second threshold flag of the present invention may indicate whether ornot all coefficients of a partial block are smaller than a predeterminedthreshold value. The number of threshold values may be N (N>=1), where arange of threshold values may be represented by {T₀, T₁, T₂, . . . ,T_(N-1)}. Here, the 0th threshold value T₀ may denote a maximum value,and the (N−1)-th threshold value T_(N-1) may denotes a minimum value,and {T₀, T₁, T₂, . . . , T_(N-1)} may be those in which the thresholdvalues are arranged in descending order. The number of threshold valuesmay be predetermined in an image decoding device or may be determinedbased on information on the number of threshold values signaled by animage encoding device.

The threshold value may be obtained by setting a maximum value to m anddecreasing the minimum value by n (n>=1). The m may be predetermined inthe image decoding apparatus or may be determined based on informationon a maximum value (m) signaled by an image encoding device. Thethreshold value may be predetermined in an image decoding device or maybe determined based on information on a threshold value signaled by animage encoding device.

A range of threshold values may be determined differently based on atleast one of a quantization parameter, a size/shape of a block, or arange of pixel values, as described in the embodiment of FIG. 9.

Referring to FIG. 10, the second threshold value flag related to acurrent threshold value may be decoded (S1000).

The second threshold value flag may indicate whether absolute values ofall coefficients of a partial block are smaller than a current thresholdvalue. For example, when the second threshold flag is “false”, it mayindicate that absolute values of all coefficients of a partial block aregreater than or equal to a current threshold value. In addition, whenthe second threshold flag is “true”, it may indicate that absolutevalues of all coefficients of a partial block are smaller than a currentthreshold value.

When the second threshold value flag is “true”, a current thresholdvalue (i-th threshold value) is updated to the next threshold value((i+1)-th threshold value) (S1010), and the above-described step S1000may be performed based on the updated current threshold value.

In addition, when the second threshold value flag is “false”, thedecoding for the second threshold value flag may not be performed anymore.

When the current threshold value reaches a minimum value of thresholdvalues or when the number of threshold values is 1, the currentthreshold value may be updated by subtracting a predetermined constantfrom the current threshold value. The predetermined constant may be aninteger greater than or equal to 1. Here, the update may be repeatedlyperformed until a second threshold value flag that is “false” isdecoded. Alternatively, when the current threshold value reaches aminimum value of threshold values or when the number of threshold valuesis 1, the updating procedure may be terminated.

As described above, when a second threshold value flag for the i-ththreshold value is “true”, this may indicate that absolute values of allcoefficients in a partial block are smaller than the i-th thresholdvalue. In addition, when a second threshold flag for the i-th thresholdis “false”, this may indicate that at least one of absolute values ofall coefficients in a partial block is greater than or equal to the i-ththreshold.

According to the decoded second threshold value flag, at least one ofsteps S700 to S750 described above may be omitted.

For example, when a range of threshold values is {5, 3}, at least one ofa second threshold value flag for the threshold value “5” or a secondthreshold value flag for the threshold value “3” may be decoded. Whenthe second threshold flag for the threshold value “5” is “false”, atleast one of absolute values of all coefficients in a partial block maybe greater than or equal to 5. In this case, coefficient of a partialblock may be decoded by performing steps S710 to S750 described above,or coefficients of a partial block may be decoded by performing theremaining steps except step S700.

When the second threshold flag for the threshold value “5” is “true”,the second threshold value flag for the threshold value “3” may bedecoded. When the second threshold flag for the threshold value “3” is“true”, absolute values of coefficients in a partial block may fallwithin the range of 0 to 2. In this case, coefficients of a partialblock may be decoded by performing the remaining steps except at leastone of the steps S730 or S740 described above, or coefficients of apartial block may be decoded by performing the remaining steps except atleast one of the steps S700, S730 or S740.

In addition, when the second threshold value flag for the thresholdvalue “3” is “false”, at least one of absolute values of allcoefficients in a partial block may be equal to or greater than 3. Inthis case, coefficients of a partial block may be decoded by performingthe above-described steps S700 to S750 in the same manner, orcoefficients of a partial block may be encoded by performing theremaining steps except step S700.

In addition, the second threshold flag of a current partial block may bederived based on the second threshold flag of another partial block. Inthis case, the second threshold flag decoding procedure may be omitted,and this will be described with reference to FIG. 11.

FIG. 11 is a diagram illustrating a method of deriving a first/secondthreshold value flag for a current partial block as an embodiment towhich the present invention is applied.

In this embodiment, it is assumed that a transform block 1100 is 8×8, apartial block is 4×4, a block including a non-zero coefficient that isfirst appeared is 1120, and partial blocks of the transform block areencoded/decoded in an order of 1140, 1120, 1130, 1110 depending on scantype.

In a current partial block, a first threshold value flag for aparticular threshold value may be derived based on a first thresholdvalue flag of a previous partial block. For example, based on a firstthreshold value flag that is “false” in a previous partial block, afirst threshold value flag of a current partial block may be derived as“false”. Here, it is assumed that {3, 5, 7} is used as a range ofthreshold values.

Specifically, since the partial block 1140 which is a first place in theencoding/decoding order has earlier encoding/decoding order than aposition of the partial block 1120 to which a non-zero coefficient thatis first appeared belongs, a first threshold value flag may not beencoded/decoded. In the partial block 1120 which is a second place inthe encoding/decoding order, since the first threshold value flag forthe threshold value “3” is “true”, only the first threshold flag for thethreshold value “3” may be encoded/decoded. In the partial block 1130which is a third place in the encoding/decoding order, since the firstthreshold value flag for the threshold value “3” is “false” and thefirst threshold value flag for the threshold value “5” is “true”, thefirst threshold flags for the threshold value “3” and “5” may berespectively encoded/decoded. In the partial block 1110 which is a lastplace in the encoding/decoding order, the first threshold value flag forthe threshold value “3” is “false” and the first threshold value flagfor the threshold value “5” is “false”. Here, since the first thresholdflag for the threshold value “3” in the previous partial block 1130 is“false”, it may be expected that the current partial block 1110 has atleast one coefficient that has absolute value equal to or greater than3, the first threshold value flag for the threshold value “3” may bederived as “false”.

In a current partial block, a first threshold value flag for aparticular threshold value may be derived based on a first thresholdvalue flag of a previous partial block. For example, based on a firstthreshold value flag that is “false” in a previous partial block, thefirst threshold value flag of the current partial block may be derived“false”.

In the present embodiment, for convenience of explanation, a transformblock 1100 is 8×8, a partial block is 4×4, the range of threshold valuesis {3, 5, 7}, and a block including the non-zero coefficient that isfirst appeared is 1120, and partial blocks of the transform block areencoded/decoded in an order of 1140, 1120, 1130, 1110 depending on scantype.

Likewise, in a current partial block, a second threshold value flag fora specific threshold value may be derived based on a second thresholdvalue flag of a previous partial block. For example, based on a firstthreshold flag that is “false” in a previous partial block, a firstthreshold flag of a current partial block may be derived as “false”.Here, it is assumed that {7, 5, 3} is used as a range of the thresholdvalues.

Specifically, since the partial block 1140 which is a first place in theencoding/decoding order has earlier encoding/decoding order than aposition of the partial block 1120 to which a non-zero coefficient thatis first appeared belongs, a second threshold value flag may not beencoded/decoded. In the partial block 1120 which is a second place inthe encoding/decoding order, since the second threshold value flag forthe threshold value “7” is “true”, the second threshold value flag forthe threshold value “5” is “true”, and the second threshold value flagfor the threshold value “3” is “true”, the second threshold flags forthe threshold value “7”, “5” and “3” may be respectivelyencoded/decoded. In the partial block 1130 which is a third place in theencoding/decoding order, since the second threshold value flag for thethreshold value “7” and “5” is respectively “true”, and the secondthreshold value flag for the threshold value “3” is “false”. In thepartial block 1110 which is a last place in the encoding/decoding order,the second threshold value flag for the threshold value “3” is “false”.Here, using that the second threshold value flag for the threshold value“3” is “false” in the previous partial block 1130, in the currentpartial block 1110, the second threshold value flag for the thresholdvalue “3” may not be encoded/decoded and may be derived as “false”.

FIG. 12 is a diagram illustrating a method of encoding coefficients of atransform block as an embodiment to which the present invention isapplied.

In an image encoding device, coefficients of a transform block may beencoded in units of a predetermined block unit (hereinafter, referred toas a partial block). A transform block may include one or more partialblocks. The partial block may be a block of N×M size. Here, N and M arenatural numbers, and N and M may be the same or different from eachother. That is, a partial block may be a square or a non-square block. Asize/shape of a partial block may be fixed (e.g., 4×4) predefined in animage encoding device, or may be variably determined according to asize/shape of a transform block. Alternatively, an image encoding devicemay determine an optimal size/shape of a partial block in considerationof an encoding efficiency, and encode the partial block. Information ona size/shape of an encoded partial block may be signaled in a level ofat least one of a sequence, a picture, a slice or a block.

An order of encoding partial blocks included in a transform block may bedetermined according to a predetermined scan type (hereinafter, referredto as a first scan type) in an image encoding device. In addition, anorder of encoding coefficients included in a partial block may bedetermined according to a predetermined scan type (hereinafter, referredto as a second scan type). The first scan type and the second scan typemay be the same or different. For the first/second scan type, a diagonalscan, a vertical scan, or a horizontal scan and the like may be used.However, the present invention is not limited thereto, and one or morescan types having predetermined angles may be further added. Thefirst/second scan type may be determined based on at least one of codingblock related information (e.g., maximum/minimum size, partitioningtechnique, etc.), size/shape of transform block, size/shape of partialblock, prediction mode, intra-prediction related information (e.g., avalue of intra-prediction mode, directionality, angle, etc.) orinter-prediction related information.

An image encoding device may encode, in a transform block, positioninformation of a coefficient (hereinafter, referred to as a non-zerocoefficient) having non-zero value first appeared in the above-describedencoding order. Encoding may be performed sequentially from a partialblock including the non-zero coefficient. Hereinafter, referring to FIG.12, a procedure of encoding coefficients of a partial block will bedescribed.

A partial block flag for a current partial block may be encoded (S1200).The partial block flag may be encoded in units of a partial block. Thepartial block flag may indicate whether there is at least one non-zerocoefficient in the current partial block. For example, when the partialblock flag is a first value, it may indicate that the current partialblock includes at least one non-zero coefficient, and when the partialblock flag is a second value, it may indicate that all coefficients ofthe current partial block are 0.

A partial block coefficient flag for a current partial block may beencoded (S1210). The partial block coefficient flag may be encoded inunits of a coefficient. The partial block coefficient flag may indicatewhether a coefficient is a non-zero coefficient. For example, when thecoefficient is a non-zero coefficient, the partial block coefficientflag may be encoded to a first value, and when the coefficient is zero,the partial block coefficient flag may be encoded to a second value. Thepartial block coefficient flag may be selectively encoded according tothe partial block flag. For example, a current partial block may beencoded for each coefficient of a partial block only when there is atleast one non-zero coefficient present in the current partial block(i.e., the partial block flag is a first value).

A flag (hereinafter, referred to as a first flag) indicating whether anabsolute value of a coefficient is greater than 1 may be encoded(S1220). The first flag may be selectively encoded according to a valueof the partial block coefficient flag. For example, when the coefficientis a non-zero coefficient (i.e., the partial block coefficient flag is afirst value), the first flag may be encoded by checking whether anabsolute value of the coefficient is greater than 1. When the absolutevalue of the coefficient is greater than 1, the first flag is encoded toa first value, and when the absolute value of the coefficient is notgreater than 1, the first flag may be encoded to a second value.

A flag (hereinafter, referred to as a second flag) indicating whether anabsolute value of a coefficient is greater than 2 may be encoded(S1230). The second flag may be selectively encoded according to a valueof the first flag. For example, when the coefficient is greater than 1(i.e., the first flag is a first value), the second flag may be encodedby checking whether an absolute value of the coefficient is greater than2. When the absolute value of the coefficient is greater than 2, thesecond flag is encoded to a first value, and when the absolute value ofthe coefficient is not greater than 2, the second flag may be encoded toa second value.

The number of at least one of the first flag or the second flag may beat least one to at most N*M. Alternatively, at least one of the firstflag or the second flag may be a fixed number (e.g., one, two, or more)predefined in an image encoding device. The number of the first/secondflag may be different depending on a block size/depth, a partitioningtechnique (e.g., quad tree, binary tree), a transforming technique(e.g., DCT, DST), whether to skip transform, quantization parameters,prediction mode (e.g., intra/inter mode), and so on. In addition to thefirst/second flag, an n-th flag indicating whether an absolute value ofa coefficient is greater than n may be additionally encoded. Here, n maymean a natural number greater than two. The number of the n-th flag maybe one, two, or more, and may be determined in the same/similar manneras the first/second flag described above.

Remaining coefficients that are not encoded based on the first/secondflag may be encoded in a current partial block (S1240). Here, theencoding may be a procedure of encoding the coefficient value itself.The remaining coefficients may be equal to or greater than two. Theremaining coefficient may be encoded based on at least one of a partialblock coefficient flag, a first flag or a second flag for the remainingcoefficient. For example, the remaining coefficient may be encoded to avalue obtained by subtracting (partial block coefficient flag+firstflag+second flag) from an absolute value of the remaining coefficient.

A sign for a coefficient of a partial block may be encoded (S1250). Thesign may be encoded in a flag format in units of a coefficient. The signmay be selectively encoded according to a value of the partial blockcoefficient flag described above. For example, the sign may be encodedonly when the coefficient is a non-zero coefficient (i.e., the partialblock coefficient flag is a first value).

As described above, each of absolute values of coefficients of thepartial block may be encoded through at least one of encoding a partialblock coefficient flag, encoding a first flag, encoding a second flag,or encoding a remaining coefficient.

In addition, above-described encoding coefficients of a partial blockmay further include a procedure of specifying a range of coefficientvalues belonging to the partial block. Through the above procedure, itmay be confirmed whether or not at least one non-zero coefficient existsin a partial block. The above procedure may be implemented throughencoding a first threshold value flag which will be described below. Theabove procedure may be implemented by being included in any one of theabove-described steps S1200 to S1250, or may be implemented in a formthat is substituted for at least one of steps S1200 to S1250.Hereinafter, the procedure of specifying a range of coefficient valuesbelonging to a partial block will be described in detail with referenceto FIG. 13.

FIG. 13 is a diagram illustrating a method of encoding a first thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

A first threshold value flag of the present invention may indicatewhether or not all coefficients of a partial block are smaller than apredetermined threshold value. The number of threshold values may be N(N>=1), where a range of threshold values may be represented by {T₀, T₁,T₂, . . . , T_(N-1)}. Here, the 0th threshold value T₀ denotes a minimumvalue, and the (N−1)-th threshold value T_(N-1) denotes a maximum value,and {T₀, T₁, T₂, . . . , T_(N-1)} may be those in which the thresholdvalues are arranged in ascending order. The number of the thresholdvalues may be predetermined in an image encoding device. The imageencoding device may determine an optimal number of threshold values inconsideration of encoding

The threshold value may be obtained by setting the minimum value to 1and increasing the minimum value by n (n>=1). The threshold value may bepredetermined in an image encoding device. The image encoding device maydetermine an optimal threshold value in consideration of the encodingefficiency and encode the threshold value.

The range of the threshold value may be determined differently dependingon a quantization parameter (QP). The QP may be set at a level of atleast one of a sequence, a picture, a slice, or a transform block.

For example, when the QP is greater than a predetermined QP threshold,it may be expected that the distribution of zero coefficients in atransform block will be higher. In this case, the range of the thresholdvalue may be determined as {3}, or the encoding procedure of the firstthreshold value flag may be omitted, and coefficients of a partial blockmay be encoded through steps S1200 to S1250 described above.

When the QP is smaller than a predetermined QP threshold, it may beexpected that the distribution of non-zero coefficients in a transformblock will be higher. In this case, the range of the threshold value maybe determined as {3, 5} or {5, 3}.

That is, the range of threshold values when QP is small may have thenumber and/or size (e.g., maximum value) of the threshold valuesdifferent from the threshold value range when QP is large. The number ofQP threshold values may be one, two, or more. The QP threshold value maybe predetermined in an image encoding device. For example, the QPthreshold value may correspond to a median value of a range of QPsavailable in the image encoding device. Alternatively, the imageencoding device may determine an optimal QP threshold value consideringencoding efficiency, and encode the QP threshold value.

Alternatively, a range of threshold values may be determined differentlydepending on the size/shape of a block. Here, a block may mean a codingblock, a prediction block, a transform block, or a partial block. Thesize may be represented by at least one of a width, a height, a sum of awidth and a height, or the number of coefficient.

For example, when a size of a block is smaller than a predeterminedthreshold size, a range of threshold values may be determined as {3}, orthe encoding procedure of the first threshold value flag may be omitted,and coefficients of a partial block may be encoded through steps S1200to S1250 described above. When a size of a block is larger than apredetermined threshold size, a range of threshold values may bedetermined as {3, 5} or {5, 3}.

That is, the range of threshold values when a block size is small mayhave the number and/or size (e.g., maximum value) of the thresholdvalues different from the threshold value range when a block size islarge. The number of threshold size may be one, two, or more. Thethreshold size may be predetermined in an image encoding device. Forexample, the threshold size may be represented by a×b, wherein a and bare 2, 4, 8, 16, 32, 64 or more, and a and b may be equal to ordifferent from each other. Alternatively, the image encoding device maydetermine an optimal threshold size considering encoding efficiency, andencode the threshold size.

Alternatively, the range of threshold values may be determineddifferently depending on a range of pixel values. The range of pixelvalues may be represented by a maximum value and/or a minimum value ofpixels belonging to a predetermined region. Here, the predeterminedregion may mean at least one of a sequence, a picture, a slice, or ablock.

For example, when the difference between the maximum value and theminimum value of the range of pixel values is smaller than apredetermined threshold difference value, the range of threshold valuesis determined as {3}, or the encoding procedure of the first thresholdvalue flag may be omitted, and coefficients of a partial block may beencoded through steps S1200 to S1250 described above. When thedifference is larger than a predetermined threshold difference value,the range of threshold values may be determined as {3, 5} or {5, 3}.

That is, the range of threshold values when the difference is small mayhave the number and/or size (e.g., maximum value) of the thresholdvalues different from a range of threshold values when the difference islarge. The number of threshold difference values may be one, two, ormore. The threshold difference value may be predetermined in an imageencoding device. Alternatively, the image encoding device may determinean optimal threshold difference value considering encoding efficiency,and encode the threshold difference value.

Referring to FIG. 13, it may be determined whether absolute values ofall coefficients in a current partial block is smaller than a currentthreshold value (S1300).

When the absolute values of all coefficients are not smaller than thecurrent threshold value, a first threshold value flag may be encoded as“false” (S1310). In this case, the current threshold value (i-ththreshold value) may be updated to the next threshold value ((i+1)-ththreshold value) (S1320), and the above described step S500 may beperformed based on the updated current threshold value. Alternatively,when absolute values of all coefficients are not smaller than thecurrent threshold value, the first threshold value flag encodingprocedure of step S1310 may be omitted, and the current threshold valuemay be updated to the next threshold value.

When the current threshold value reaches a maximum value of a thresholdvalue or when the number of the threshold values is 1, the currentthreshold value may be updated by adding a predetermined constant to thecurrent threshold value. The predetermined constant may be an integergreater than or equal to one. Here, the update may be repeatedlyperformed until the first threshold value flag is encoded as “true”.Based on the updated current threshold value, step S1300 may beperformed. Alternatively, when the current threshold value reaches themaximum value of the threshold value or when the number of thresholdvalues is 1, the updating procedure may be terminated.

When absolute values of all coefficients are smaller than a currentthreshold value, the first threshold value flag may be encoded as “true”(S1330).

As described above, when the first threshold value flag for the i-ththreshold value is “true”, this may indicate that absolute values of allcoefficients in a partial block are smaller than the i-th thresholdvalue. When the first threshold value flag for the i-th threshold is“false”, this may indicate that absolute values of all coefficients inthe partial block is greater than or equal to the i-th threshold. Basedon the first threshold flag that is “true”, a range of coefficientvalues belonging to the partial block may be specified. That is, whenthe first threshold value flag for the i-th threshold value is “true”,the coefficient belonging to the partial block may fall within the rangeof 0 to (i-th threshold value−1).

According to the encoded first threshold value flag, at least one ofsteps S1200 to S1250 described above may be omitted.

For example, when a range of threshold values is {3, 5}, at least one ofthe first threshold value flag for the threshold value “3” or the firstthreshold value flag for the threshold value “5” may be encoded. Whenthe first threshold value flag for the threshold value “3” is “true”,absolute values of all coefficients in the partial block may fall withinthe range of 0 to 2. In this case, coefficients of the partial block maybe encoded by performing the remaining steps except at least one of theabove-described steps S1230 or S1240, or the coefficients of the partialblock may be encoded by performing the remaining steps except at leastone of S1200, S1230 or S1240.

When the first threshold value flag for the threshold “3” is “false”,the first threshold value flag for the threshold “5” may be encoded.When the first threshold value flag for the threshold “5” is “false”, atleast one of absolute values of coefficients in a partial block may begreater than or equal to 5. In this case, coefficients of the partialblock may be encoded by performing the above-described steps S1200 toS1250 in the same manner, or coefficients of the partial block may beencoded by performing the remaining steps except step S1200.

When the first threshold value flag for the threshold “5” is “true”,absolute values of all coefficients in the partial block may fall withinthe range of 0 to 4. In this case, coefficients of the partial block maybe encoded by performing the above-described steps S1200 to S1250 in thesame manner, or coefficients of the partial block may be encoded byperforming the remaining steps except step S1200.

In addition, a first threshold value flag of a current partial block maybe derived based on a first threshold flag of another partial block. Inthis case, the encoding procedure of the first threshold value flag maybe omitted, and this will be described with reference to FIG. 16.

FIG. 14 is a diagram illustrating a method of decoding coefficients of atransform block as an embodiment to which the present invention isapplied.

Coefficients of a transform block may be decoded in units of apredetermined block (hereinafter, referred to as a partial block) in animage decoding device. A transform block may include one or more partialblocks. A partial block may be a block of N×M size. Here, N and M arenatural numbers, and N and M may be equal to or different from eachother. That is, a partial block may be a square or a non-square block. Asize/shape of a partial block may be fixed (e.g., 4×4) predefined in animage decoding device, may be variably determined depending on asize/shape of a transform block, or may be variably determined based onsignaled information on a size/shape of a partial block. Information ona size/shape of a partial block may be signaled in a level of at leastone of a sequence, a picture, a slice or a block.

An order of decoding partial blocks belonging to a transform block maybe determined according to a predetermined scan type (hereinafter,referred to as a first scan type) in an image decoding device. Inaddition, an order of decoding coefficients belonging to a partial blockmay be determined according to a predetermined scan type (hereinafter,referred to as a second scan type). The first scan type and the secondscan type may be the same or different. For the first/second scan type,a diagonal scan, a vertical scan, a horizontal scan and the like may beused. However, the present invention is not limited thereto, and one ormore scan types having predetermined angles may be further added. Thefirst/second scan type may be determined based on at least one of codingblock related information (e.g., maximum/minimum size, partitioningtechnique, etc.), size/shape of transform block, size/shape of partialblock, prediction mode, intra-prediction related information (e.g., avalue of intra-prediction mode, directionality, angle, etc.) orinter-prediction related information.

An image decoding device may decode, in a transform block, positioninformation of a coefficient (hereinafter, referred to as a non-zerocoefficient) having non-zero value first appeared in the above-describeddecoding order. Decoding may be performed sequentially from a partialblock according to the position information. Hereinafter, a procedure ofdecoding coefficients of a partial block will be described withreference to FIG. 14.

A partial block flag for a current partial block may be decoded (S1400).The partial block flag may be decoded in units of a partial block. Thepartial block flag may indicate whether there is at least one non-zerocoefficient in the current partial block. For example, when the partialblock flag is a first value, it may indicate that the current partialblock includes at least one non-zero coefficient, and when the partialblock flag is a second value, it may indicate that all coefficients ofthe current partial block are 0.

A partial block coefficient flag for a current partial block may bedecoded (S1410). The partial block coefficient flag may be decoded inunits of a coefficient. The partial block coefficient flag may indicatewhether the coefficient is a non-zero coefficient. For example, when thepartial block coefficient flag is a first value, it may indicate thatthe coefficient is a non-zero coefficient, and when the partial blockcoefficient flag is a second value, it may indicate that the coefficientis zero. The partial block coefficient flag may be selectively decodedaccording to the partial block flag. For example, a current partialblock may be decoded for each coefficient of a partial block only whenthere is at least one non-zero coefficient present in the currentpartial block (i.e., the partial block flag is a first value).

A flag (hereinafter, referred to as a first flag) indicating whether anabsolute value of a coefficient is greater than 1 may be decoded(S1420). The first flag may be selectively decoded according to a valueof the partial block coefficient flag. For example, when the coefficientis a non-zero coefficient (i.e., the partial block coefficient flag is afirst value), the first flag may be decoded to check whether theabsolute value of the coefficient is greater than 1. When the first flagis a first value, the absolute value of the coefficient is greater than1, and when the first flag is a second value, the absolute value of thecoefficient may be 1.

A flag (hereinafter, referred to as a second flag) indicating whether anabsolute value of a coefficient is greater than 2 may be decoded(S1430). The second flag may be selectively decoded according to a valueof the first flag. For example, when the coefficient is greater than 1(i.e., the first flag is a first value), the second flag may be decodedto check whether the absolute value of the coefficient is greater than2. When the second flag is a first value, the absolute value of thecoefficient is greater than 2, and when the second flag is a secondvalue, the absolute value of the coefficient may be 2.

The number of at least one of the first flag or the second flag may beat least one to at most N*M. Alternatively, at least one of the firstflag or the second flag may be a fixed number (e.g., one, two, or more)predefined in an image decoding device. The number of the first/secondflag may be different depending on a block size/depth, a partitioningtechnique (e.g., quad tree, binary tree), a transforming technique(e.g., DCT, DST), whether to skip transform, quantization parameters,prediction mode (e.g., intra/inter mode), and so on. In addition to thefirst/second flag, an n-th flag indicating whether an absolute value ofa coefficient is greater than n may be additionally decoded. Here, n maymean a natural number greater than two. The number of the n-th flag maybe one, two, or more, and may be determined in the same/similar manneras the first/second flag described above.

Remaining coefficients that are not decoded based on the first/secondflag may be decoded in a current partial block (S1440). Here, thedecoding may be a procedure of decoding the coefficient value itself.The remaining coefficients may be equal to or greater than two. Theremaining coefficient may be encoded based on at least one of a partialblock coefficient flag, a first flag or a second flag for the remainingcoefficient. For example, the remaining coefficient may be encoded to avalue obtained by subtracting (partial block coefficient flag+firstflag+second flag) from an absolute value of the remaining coefficient.

A sign for a coefficient of a partial block may be decoded (S1450). Thesign may be decoded in a flag format in units of a coefficient. The signmay be selectively decoded according to a value of the partial blockcoefficient flag described above. For example, the sign may be decodedonly when the coefficient is a non-zero coefficient (i.e., the partialblock coefficient flag is a first value).

In addition, above-described decoding coefficients of a partial blockmay further include a procedure of specifying a range of coefficientvalues belonging to the partial block. Through the above procedure, itmay be confirmed whether or not at least one non-zero coefficient existsin a partial block. The above procedure may be implemented throughdecoding a first threshold value flag which will be described below. Theabove procedure may be implemented by being included in any one of theabove-described steps S1400 to S1450, or may be implemented in a formthat is substituted for at least one of steps S1400 to S1450.Hereinafter, the procedure of specifying a range of coefficient valuesbelonging to a partial block will be described in detail with referenceto FIG. 15.

FIG. 15 is a diagram illustrating a method of decoding a first thresholdvalue flag for a partial block as an embodiment to which the presentinvention is applied.

A first threshold flag of the present invention may indicate whether ornot all coefficients of a partial block are smaller than a predeterminedthreshold value. The number of threshold values may be N (N>=1), where arange of threshold values may be represented by {T₀, T₁, T₂, . . . ,T_(N-1)}. Here, the 0th threshold value T₀ may denote a minimum value,and the (N−1)-th threshold value T_(N-1) may denotes a maximum value,and {T₀, T₁, T₂, . . . , T_(N-1)} may be those in which the thresholdvalues are arranged in ascending order. The number of threshold valuesmay be predetermined in an image decoding device or may be determinedbased on signaled information on the number of threshold values.

The threshold value may be obtained by setting a minimum value to 1 andincreasing the minimum value by n (n>=1). The threshold value may be setin an image decoding device or may be determined based on signaledinformation on a threshold value.

A range of threshold values may be determined differently depending on aquantization parameter (QP). The QP may be set at a level of at leastone of a sequence, a picture, a slice, or a transform block.

For example, when the QP is larger than a predetermined QP thresholdvalue, a range of threshold values may be determined as {3}, or thefirst threshold value flag decoding procedure may be omitted, andthrough the above-described steps of S1400 to S1450 coefficients of apartial block may be decoded.

In addition, when the QP is smaller than a predetermined QP threshold, arange of threshold values may be determined as {3, 5} or {5, 3}.

That is, a range of threshold values when the QP is small may have thenumber and/or size (e.g., maximum value) of threshold values differentfrom a range of threshold values when the QP is large. The number of QPthreshold values may be one, two, or more. The QP threshold value may beset in an image decoding device. For example, the QP threshold value maycorrespond to a median value of a range of QPs available in an imagedecoding device. Alternatively, the QP threshold value may be determinedbased on information on the QP threshold value signaled by an imageencoding device.

Alternatively, a range of threshold values may be determined differentlydepending on a size/shape of a block. Here, a block may mean a codingblock, a prediction block, a transform block, or a partial block. Thesize may be represented by at least one of a width, a height, a sum of awidth and a height, or the number of coefficients.

For example, when a block size is smaller than a predetermined thresholdsize, a range of threshold values may be determined as {3}, or the firstthreshold value flag decoding procedure may be omitted, and coefficientsof a partial block may be decoded through steps S1400 to S1450 describedabove. In addition, when a block size is larger than a predeterminedthreshold size, a range of threshold values may be determined as {3, 5}or {5, 3}.

That is, a range of threshold values when a block size is small may havethe number and/or size (e.g., maximum value) of threshold valuesdifferent from a range of threshold values when a block size is large.The number of threshold size may be one, two, or more. The thresholdsize may be set in an image decoding device. For example, the thresholdsize may be represented by a×b, where a and b are 2, 4, 8, 16, 32, 64 ormore, and a and b may be the same or different. Alternatively, thethreshold size may be determined based on information on a thresholdsize signaled by an image encoding device.

Alternatively, a range of threshold values may be determined differentlydepending on a range of pixel values. The range of pixel values may berepresented by a maximum value and/or a minimum value of pixelsbelonging to a predetermined region. Here, the predetermined region maymean at least one of a sequence, a picture, a slice, or a block.

For example, when a difference between a maximum value and a minimumvalue of a range of pixel values is smaller than a predeterminedthreshold difference value, a range of threshold values may bedetermined as {3}, or the first threshold value flag decoding proceduremay be omitted, and coefficients of a partial block may be decodedthrough steps S1400 to S1450 described above. In addition, when thedifference is larger than a predetermined threshold difference value,the range of threshold values may be determined as {3, 5} or {5, 3}.

That is, a range of threshold values when the difference is small mayhave the number and/or size (e.g., maximum value) of threshold valuesdifferent from a range of threshold values when the difference is large.The number of threshold difference values may be one, two, or more. Thethreshold difference value may be set in an image decoding device or maybe determined based on information on a threshold difference valuesignaled by an image encoding device.

Referring to FIG. 15, a first threshold value flag for a currentthreshold value may be decoded (S1500).

The first threshold value flag may indicate whether absolute values ofall coefficients of a partial block are smaller than a current thresholdvalue. For example, when the first threshold value flag is “false”, itmay indicate that absolute values of all coefficients of a partial blockare greater than or equal to a current threshold. In addition, when thefirst threshold value flag is “true”, it may indicate that absolutevalues of all coefficients of a partial block are smaller than a currentthreshold value.

When the first threshold value flag is “false”, the current thresholdvalue (i-th threshold value) may be updated to the next threshold value((i+1-th threshold value) (S1510), based on the updated currentthreshold value, step S1500 described above may be performed.

When the current threshold value reaches a maximum value of thresholdvalues or when the number of threshold values is 1, the currentthreshold value may be updated by adding a predetermined constant to thecurrent threshold value. The predetermined constant may be an integergreater than or equal to one. Here, the update may be repeatedlyperformed until the first threshold value that is “true” is decoded.Alternatively, when the current threshold value reaches a maximum valueof threshold values or when the number of threshold values is 1, theupdating procedure may be terminated.

As shown in FIG. 15, when the first threshold value flag is “true”,decoding of a first threshold value flag may not be performed any more.

As described above, when a first threshold value flag for the i-ththreshold value is “true”, it may indicate that absolute values of allcoefficients in a partial block are smaller than the i-th thresholdvalue. In addition, when a first threshold flag for the i-th thresholdvalue is “false”, it may indicate that absolute values of allcoefficients in a partial block are greater than or equal to the i-ththreshold value. Based on the first threshold value flag that is “true”,a range of coefficient values belonging to a partial block may bespecified. That is, when a first threshold value flag for the i-ththreshold value is “true”, a coefficient belonging to a partial blockmay fall within a range of 0 to (i-th threshold value−1).

According to the decoded first threshold value flag, at least one ofsteps S1400 to S1450 described above may be omitted.

For example, when a range of threshold values is {3, 5}, at least one ofa first threshold value flag for the threshold value “3” or a firstthreshold value flag for the threshold value “5” may be decoded. Whenthe first threshold value flag for the threshold value “3” is “true”,absolute values of all coefficients in a partial block may fall withinthe range of 0 to 2. In this case, coefficients of a partial block maybe decoded by performing the remaining steps except at least one of thesteps S1430 or S1440 described above, or coefficients of a partial blockmay be decoded by performing the remaining steps except at least one ofthe steps S1400, S1430 or S1440 described above.

When the first threshold value flag for the threshold value “3” is“false”, the first threshold value flag for the threshold value “5” maybe decoded. When the first threshold value flag for the threshold value“5” is “false”, at least one of absolute values of coefficients in apartial block may be greater than or equal to 5. In this case,coefficients of a partial block may be decoded by performing theabove-described steps S1400 to S1450 in the same manner, or coefficientsof a partial block may be decoded by performing the remaining stepsexcept step S1400.

In addition, when the first threshold value flag for the threshold value“5” is “true”, absolute values of all coefficients in a partial blockmay fall within the range of 0 to 4. In this case, coefficients of apartial block may be decoded by performing the above-described stepsS1400 to S1450 in the same manner, or coefficients of a partial blockmay be decoded by performing the remaining steps except step S1400.

In addition, a first threshold value flag of a current partial block maybe derived based on a first threshold value flag of another partialblock. In this case, decoding procedure for a first threshold value flagmay be omitted, and this will be described with reference to FIG. 16.

FIG. 16 is a diagram illustrating a method of deriving a first thresholdvalue flag for a current partial block as an embodiment to which thepresent invention is applied.

In this embodiment, it is assumed that a transform block 1600 is 8×8, apartial block is 4×4, a block including a non-zero coefficient that isfirst appeared is 1620, and partial blocks of the transform block areencoded/decoded in an order of 1640, 1620, 1630, 1610 depending on scantype.

In a current partial block, a first threshold value flag for aparticular threshold value may be derived based on a first thresholdvalue flag of a previous partial block. For example, based on a firstthreshold value flag that is “false” in a previous partial block, afirst threshold value flag of a current partial block may be derived as“false”. Here, it is assumed that {3, 5, 7} is used as a range ofthreshold values.

Specifically, since the partial block 1640 which is a first place in theencoding/decoding order has earlier encoding/decoding order than aposition of the partial block 1620 to which a non-zero coefficient thatis first appeared belongs, a first threshold value flag may not beencoded/decoded. In the partial block 1620 which is a second place inthe encoding/decoding order, since the first threshold value flag forthe threshold value “3” is “true”, only the first threshold flag for thethreshold value “3” may be encoded/decoded. In the partial block 1630which is a third place in the encoding/decoding order, since the firstthreshold value flag for the threshold value “3” is “false” and thefirst threshold value flag for the threshold value “5” is “true”, thefirst threshold flags for the threshold value “3” and “5” may berespectively encoded/decoded. In the partial block 1610 which is a lastplace in the encoding/decoding order, the first threshold value flag forthe threshold value “3” is “false” and the first threshold value flagfor the threshold value “5” is “false”. Here, since the first thresholdflag for the threshold value “3” in the previous partial block 1630 is“false”, it may be expected that the current partial block 1610 has atleast one coefficient that has absolute value equal to or greater than3, the first threshold value flag for the threshold value “3” may bederived as “false”.

In a current partial block, a first threshold value flag for aparticular threshold value may be derived based on a first thresholdvalue flag of a previous partial block. For example, based on a firstthreshold value flag that is “false” in a previous partial block, thefirst threshold value flag of the current partial block may be derived“false”.

Hereinafter, a method of determining a partial block of a transformblock will be described in detail.

An image encoding device may determine a partial block having apredetermined size/shape constituting a transform block, and may encodeinformation on the size/shape of the partial block. An image decodingdevice may determine a size/shape of a partial block based on theencoded information (first method). Alternatively, a size/shape of apartial block may be determined through a predetermined rule in an imageencoding/decoding device (second method). Information indicating whetherto determine a size/shape of a partial block through which one of thefirst and second methods may be signaled in at least one layer of avideo, a sequence, a picture, a slice, or a block. The block may referto a coding block, a prediction block or a transform block.

A size of a partial block in a transform block may be equal to orsmaller than a size of the transform block. A shape of the transformblock/partial block may be square or non-square. A shape of a transformblock may be the same as or different from a shape of a partial block.

Information on a shape of a transform block may be encoded. Here, theinformation may include at least one of information on whether to useonly a square, a non-square, or both a square and a non-square for ashape of a transform block. The information may be signaled in at leastone layer of a video, a sequence, a picture, a slice, or a block. Theblock may refer to a coding block, a prediction block, or a transformblock. Information on a size of a transform block may be encoded. Here,the information may include at least one of a minimum size, a maximumsize, a partitioning depth or a maximum/minimum value for a partitioningdepth. The information may be signaled in at least one layer of a video,a sequence, a picture, a slice, or a block.

Information on a shape of a partial block may be encoded. Here, theinformation may include at least one of information on whether to useonly a square, a non-square, or both a square and a non-square for ashape of a partial block. The information may be signaled in at leastone layer of a video, a sequence, a picture, a slice, or a block. Theblock may refer to a coding block, a prediction block, or a transformblock. Information on a size of a partial block may be encoded. Here,the information may include at least one of a minimum size, a maximumsize, a partitioning depth, and a maximum/minimum value for apartitioning depth. The information may be signaled in at least onelayer of a video, a sequence, a picture, a slice, or a block.

FIG. 17 is a diagram illustrating a method of determining a size/shapeof a partial block based on partitioning index information as anembodiment to which the present invention is applied.

An image encoding device may determine which partitioning format of apartial block is the most optimal through RDO, from when all partialblocks of a transform block have maximum size until when all partialblocks have minimum size.

Referring to FIG. 17, a transform block 1701 is composed of one partialblock 1, and an RD-cost value in this case may be calculated. Thepartial block 1 may be a partial block of a maximum size predefined inan image encoding device. A transform block 1702 is a case where thetransform block 1701 is partitioned into four partial blocks 1-4, and anRD-cost value in this case may be calculated. A transform block 1703 isa case where each partial block of the transform block 1702 is againpartitioned into four partial blocks, and an RD-cost value in this casemay be calculated.

As described above, within a range of a partial block of a maximum sizeto a minimum size, RD-cost values may be calculated while partitioning atransform block into partial blocks of the same size. An optimalpartitioning is determined based on the RD-cost values, and apartitioning index information indicating optimal partitioning may beencoded. An image decoding device may determine a size/shape of apartial block in a transform block based on the encoded partitioningindex information.

For example, when a transform block 1701 is the optimum partitioning, animage encoding device may encode “0” as a partitioning indexinformation, and when a transform block 1702 is the optimumpartitioning, an image encoding device may encode “1” as a partitioningindex information, when a transform block 1703 is the optimumpartitioning, an image encoding device may encode “2” as a partitioningindex information, respectively. An image decoding device may determinea size/shape of a partial block in a transform block based on theencoded partitioning index information.

Depending on a quantization parameter (QP) of a transform block, all orsome of partial blocks in the transform block may be selectivelyencoded/decoded. For example, when the QP of the transform block islarger than a predetermined QP threshold value, only a partial region inthe transform block may be encoded/decoded. In addition, when the QP ofthe transform block is smaller than a predetermined QP threshold value,all partial blocks in the transform block may be encoded/decoded.

Here, the partial region may be specified by at least one of apredetermined vertical line or a horizontal line. The vertical line maybe located apart from a left boundary of a transform block by a distancea to the left direction, and the horizontal line may be located apartfrom a top boundary of a transform block by a distance b to the bottomdirection. The a and b are natural numbers, and may be the same ordifferent from each other. The a may fall within a range of 0 to a widthof a transform block, and the b may fall within a range of 0 to a heightof a transform block. The partial region may be a region located on aleft side with respect to the vertical line and/or on an upper side withrespect to the horizontal line. The position of the vertical/horizontalline may be predetermined in an image encoding/decoding device, or maybe variably determined in consideration of a size/shape of a transformblock. Alternatively, an image encoding device may encode informationspecifying a partial region (e.g., information for specifying a positionof the vertical/horizontal line) and signal the information, and animage decoding device may specify a partial region based on the signaledinformation. A boundary of the specified partial region may or may notbe in contact with a boundary of a partial block in a transform block.

For example, the partial region may be one partial block of a regionwhere DC components are concentrated or N partial blocks (N 1) furtherincluding an adjacent partial block. Alternatively, the partial regionmay be specified by a vertical line crossing 1/n point of a top boundaryof a transform block and/or a horizontal line crossing 1/m point of aleft boundary of a transform block. The n and m are natural numbers andmay be the same or different from each other.

The number of QP threshold values may be one, two, or more. A QPthreshold value may be predetermined in an image encoding device. Forexample, the QP threshold value may correspond to a median value of arange of QPs available in an image encoding/decoding device.Alternatively, an image encoding device may determine an optimal QPthreshold value considering encoding efficiency, and may encode the QPthreshold.

Alternatively, depending on a size of a transform block, all or some ofpartial blocks in the transform block may be selectivelyencoded/decoded. For example, when a size of a transform block is equalto or greater than a predetermined threshold size, only a partial regionin the transform block may be encoded/decoded. In addition, when a sizeof a transform block is smaller than a predetermined threshold size, allpartial blocks in a transform block may be encoded/decoded.

Here, the partial region may be specified by at least one of apredetermined vertical line or a horizontal line. The vertical line maybe located apart from a left boundary of a transform block by a distancea to the left direction, and the horizontal line may be located apartfrom a top boundary of a transform block by a distance b to the bottomdirection. The a and b are natural numbers, and may be the same ordifferent from each other. The a may fall within a range of 0 to a widthof a transform block, and the b may fall within a range of 0 to a heightof a transform block. The partial region may be a region located on aleft side with respect to the vertical line and/or on an upper side withrespect to the horizontal line. The position of the vertical/horizontalline may be predetermined in an image encoding/decoding device, or maybe variably determined in consideration of a size/shape of a transformblock. Alternatively, an image encoding device may encode informationspecifying a partial region (e.g., information for specifying a positionof the vertical/horizontal line) and signal the information, and animage decoding device may specify a partial region based on the signaledinformation. A boundary of the specified partial region may or may notbe in contact with a boundary of a partial block in a transform block.

For example, the partial region may be one partial block of a regionwhere DC components are concentrated or N partial blocks (N≥≥1) furtherincluding an adjacent partial block. Alternatively, the partial regionmay be specified by a vertical line crossing 1/n point of a top boundaryof a transform block and/or a horizontal line crossing 1/m point of aleft boundary of a transform block. The n and m are natural numbers andmay be the same or different from each other.

The number of threshold sizes may be one, two, or more. The thresholdsize may be predetermined in an image encoding device. For example, thethreshold size may be represented by c×d, where c and d are 2, 4, 8, 16,32, 64 or more, and c and d may be the same or different. Alternatively,an image encoding device may determine an optimal threshold size inconsideration of encoding efficiency, and encode the threshold size.

Hereinafter, a method for efficiently encoding/decoding theabove-described partial block coefficient flag will be described withreference to FIG. 18 to FIG. 23.

In a frequency domain, DC component region in a transform block has ahigh probability that a partial block coefficient flag is determined as“1”, and AC component region has a high probability that a partial blockcoefficient flag is determined as “0”. In consideration of suchstatistical characteristics, a partial block coefficient flag may beencoded.

FIG. 18 is a diagram illustrating a method of encoding a partial blockcoefficient flag based on the number of non-zero coefficients in apartial block as an embodiment to which the present invention isapplied.

First, a partial block coefficient flag may be encoded with respect to acoefficient of a current partial block. That is, when the coefficient isa non-zero coefficient, the partial block coefficient flag may beencoded to a first value (e.g., “1”) and when the coefficient is 0, thepartial block coefficient flag may be encoded to a second value (e.g.,“0”). The partial block coefficient flag may be encoded for eachcoefficient belonging to a current partial block, and the number ofnon-zero coefficients belonging to a current partial block may bedetermined through the above-described procedure. A partial blockcoefficient flag of a next partial block may be encoded based on thenumber of non-zero coefficients in a current partial block.

Referring to FIG. 18, the number of non-zero coefficients in a currentpartial block may be compared with a predetermined threshold value(hereinafter, referred to as the number of NZ) (S1800). Here, the numberof NZ may be a fixed number pre-determined in an image encoding device,or may be variably determined based on a size of a transform blockand/or a partial block. For example, when a partial block is N×N, thepartial block includes (N*N) coefficients, where the number of NZ may bedetermined as a value of (N*N)/2.

Based on a comparison result of step S1800, a partial block coefficientflag for a coefficient of a next partial block may be encoded (S1810).Here, the next partial block may mean a partial block to be encoded nextto a current partial block according to an encoding order (or an orderaccording to a scan type).

For example, when the number of non-zero coefficients in the currentpartial block is larger than the number of NZ, a partial blockcoefficient flag of the next partial block may be encoded in a differentmeaning from a partial block coefficient flag of the current partialblock. That is, in the next partial block, when a coefficient is anon-zero coefficient, a partial block coefficient flag for thecoefficient may be encoded to a second value (e.g., “0”), and when thecoefficient is 0, a partial block coefficient flag for the coefficientmay be encoded to a first value (e.g., “1”).

In addition, when the number of non-zero coefficients in the currentpartial block is smaller than the number of NZ, a partial blockcoefficient flag of the next partial block may be encoded in a samemeaning as a partial block coefficient flag of the current partialblock. That is, in the next partial block, when a coefficient is anon-zero coefficient, a partial block coefficient flag for thecoefficient may be encoded to a first value (for example, “1”), and whenthe coefficient is 0, a partial block coefficient flag for thecoefficient may be encoded to a second value (e.g., “0”).

The encoding scheme described above may be performed in units of atransform block. For example, the encoding scheme may be restricted tobe performed only until the next partial block reaches a partial blockhaving a last encoding order in the transform block. However, thepresent invention is not limited thereto, and the same/similar schememay be performed when the current partial block and the next partialblock belong to different transform blocks.

When the partial block coefficient flag is encoded according to theabove-described manner, an image decoding device may determine whether acoefficient of a current partial block is a non-zero coefficient, basedon at least one of encoded partial block coefficient flag for a currentpartial block or the number of non-zero coefficients in a previouspartial block.

For example, when a partial block coefficient flag for a coefficient ofa current partial block is a first value, the coefficient may bedetermined as a non-zero coefficient, and when the partial blockcoefficient flag is a second value, the coefficient may be determined as“0”.

Here, further considering the number of non-zero coefficients in aprevious partial block, it may be finally determined whether or not thecoefficient is a non-zero coefficient. When the number of non-zerocoefficients in a previous partial block is larger than the number ofNZ, a coefficient having a partial block coefficient flag of a firstvalue may be determined as 0, and a coefficient having a partial blockcoefficient flag of a second value may be determined as a non-zerocoefficient. In addition, when the number of non-zero coefficients in aprevious partial block is smaller than the number of NZ, a firstdetermination as to whether it is a non-zero coefficient may bemaintained.

A previous partial block referred to by the current partial block may berestricted to belong to the same transform block as the current partialblock. However, the present invention is not limited thereto, and apartial block coefficient flag for a current partial block may bedecoded by referring to a partial block belonging to another transformblock.

FIG. 19 is a diagram illustrating a method of changing probabilityinformation of a partial block coefficient flag based on the number ofnon-zero coefficients in a partial block as an embodiment to which thepresent invention is applied.

An image encoding device may encode a partial block coefficient flag toa predetermined value according to whether a coefficient of a currentpartial block is a non-zero coefficient. That is, when the coefficientis a non-zero coefficient, the partial block coefficient flag may beencoded to a first value (e.g., “1”), and when the coefficient is 0, thepartial block coefficient flag may be encoded to a second value (Forexample, “0”). Further, based on the number of non-zero coefficients inthe current partial block, probability information of a partial blockcoefficient flag of a next partial block may be changed. Hereinafter,for convenience of explanation, it is assumed that a partial blockcoefficient flag is encoded/decoded based on the CABAC regular codingmethod.

Referring to FIG. 19, the number of non-zero coefficients in a currentpartial block may be compared with a predetermined threshold value(hereinafter, referred to as the number of NZ) (S1900). Here, the numberof NZ is as shown in the embodiment of FIG. 18, and a detaileddescription thereof will be omitted.

Based on a comparison result of step S1900, probability information of apartial block coefficient flag for a coefficient of a next partial blockmay be changed (S1910). Here, the next partial block may mean a partialblock to be encoded next to a current partial block according to anencoding order (or an order according to a scan type). The probabilityinformation may refer to a probability table predetermined in an imageencoding/decoding device, a probability value derived from an imageencoding/decoding device, a variable for calculating probability, andthe like.

For example, in encoding a partial block coefficient flag of a nextpartial block, when the number of non-zero coefficients in the currentpartial block is larger than the number of NZ, for the partial blockcoefficient flag of the next partial block, probability information onoccurrence of “0” and probability information on occurrence of “1” maybe exchanged with each other. In addition, when the number of non-zerocoefficients in the current partial block is smaller than the number ofNZ, for the partial block coefficient flag of the next partial block,probability information on occurrence of “0” and probability informationon occurrence of “0” may not be exchanged with each other.

The encoding scheme described above may be performed in units of atransform block. For example, the encoding scheme may be restricted tobe performed only until the next partial block reaches a partial blockhaving a last encoding order in the transform block. However, thepresent invention is not limited thereto, and the same/similar schememay be performed when the current partial block and the next partialblock belong to different transform blocks.

When the partial block coefficient flag is encoded according to theabove-described manner, an image decoding device may decode a partialblock coefficient flag of a current partial block, based on the numberof non-zero coefficients in a previous partial block.

Specifically, probability information on a partial block coefficientflag of a current partial block may be changed based on the comparisonresult of the number of non-zero coefficients in the previous block andthe number of NZ, and the partial block coefficient flag may be decodedbased on the changed probability information.

For example, when the number of non-zero coefficients in a previouspartial block is larger than the number of NZ, for the partial blockcoefficient flag, probability information on occurrence of “0” and theprobability information on occurrence of “1” may be exchanged eachother. In addition, when the number of non-zero coefficients in aprevious partial block is smaller than a number of NZ, for the partialblock coefficient flag, probability information on occurrence of “0” andthe probability information on occurrence of “1” may not be exchangedeach other.

In addition, a previous partial block referred to by the current partialblock may be restricted to belong to the same transform block as thecurrent partial block. However, the present invention is not limitedthereto, and a partial block coefficient flag for a current partialblock may be decoded by referring to a partial block belonging toanother transform block.

FIG. 20 is a diagram illustrating a method of encoding a partial blockcoefficient flag based on the number of non-zero coefficients up to acurrent coefficient as an embodiment to which the present invention isapplied.

Referring to FIG. 20, the number of non-zero coefficients up to acurrent coefficient in a current partial block may be compared with thenumber of NZ (S2000). The number of non-zero coefficients up to acurrent coefficient may be calculated according to an encoding order ofcoefficients (or an order according to a scan type). The number of NZ isas shown in the embodiment of FIG. 18, and a detailed descriptionthereof will be omitted.

Based on a comparison result of step S2000, a partial block coefficientflag for a next coefficient may be encoded (S2010). Here, the nextcoefficient may mean a coefficient to be encoded next to a currentcoefficient according to an encoding order (or an order according to ascan type).

For example, when the number of non-zero coefficients up to the currentcoefficient is larger than or equal to the number of NZ, a partial blockcoefficient flag of the next coefficient may be encoded in a differentmeaning from a partial block coefficient flag of the currentcoefficient. That is, when a next coefficient is a non-zero coefficient,a partial block coefficient flag for the next coefficient may be encodedto a second value (e.g., “0”), and when the next coefficient is 0, apartial block coefficient flag for the next coefficient may be encodedto a first value (e.g., “1”).

In addition, when the number of non-zero coefficients up to the currentcoefficient is smaller than the number of NZ, a partial blockcoefficient flag of the next coefficient may be encoded in a samemeaning as a partial block coefficient flag of the current coefficient.That is, when a next coefficient is a non-zero coefficient, a partialblock coefficient flag for the next coefficient may be encoded to afirst value (for example, “1”), and when the next coefficient is 0, apartial block coefficient flag for the next coefficient may be encodedto a second value (e.g., “0”).

The encoding scheme described above may be performed in units of atransform block or a partial block. For example, the encoding scheme maybe restricted to be performed only until the next coefficient reaches acoefficient having a last encoding order in the transform block or inthe partial block. However, the present invention is not limitedthereto, and the same/similar scheme may be performed when the currentcoefficient and the next coefficient belong to different transformblocks or different partial blocks.

When the partial block coefficient flag is encoded according to theabove-described manner, an image decoding device may determine whether acurrent coefficient is a non-zero coefficient, based on at least one ofencoded partial block coefficient flag for a current coefficient or thenumber of non-zero coefficients up to a previous coefficient.

For example, when a partial block coefficient flag for a currentcoefficient is a first value, the current coefficient may be determinedas a non-zero coefficient, and when the partial block coefficient flagis a second value, the current coefficient may be determined as “0”.

Here, further considering the number of non-zero coefficients up to aprevious coefficient in a current partial block, it may be finallydetermined whether or not the current coefficient is a non-zerocoefficient. When the number of non-zero coefficients up to a previouscoefficient is larger than the number of NZ, a current coefficienthaving a partial block coefficient flag of a first value may bedetermined as 0, and a current coefficient having a partial blockcoefficient flag of a second value may be determined as a non-zerocoefficient. In addition, when the number of non-zero coefficients up toa previous coefficient is smaller than the number of NZ, a firstdetermination as to whether it is a non-zero coefficient may bemaintained.

In addition, a previous coefficient referred to by the currentcoefficient may be restricted to belong to the same partial block as thecurrent coefficient. However, the present invention is not limitedthereto, and a current coefficient may refer to a coefficient thatbelongs to another partial block or another transform block.

FIG. 21 is a diagram illustrating a method of changing probabilityinformation of a partial block coefficient flag based on the number ofnon-zero coefficients up to a current coefficient as an embodiment towhich the present invention is applied.

An image encoding device may encode a partial block coefficient flag toa predetermined value according to whether a coefficient of a currentpartial block is a non-zero coefficient. That is, when the coefficientis a non-zero coefficient, the partial block coefficient flag may beencoded to a first value (e.g., “1”), and when the coefficient is 0, thepartial block coefficient flag may be encoded to a second value (Forexample, “0”). Here, in the current partial block, based on the numberof non-zero coefficients up to the current coefficient, probabilityinformation of a partial block coefficient flag of a next coefficientmay be changed. Hereinafter, for convenience of explanation, it isassumed that a partial block coefficient flag is encoded/decoded basedon the CABAC regular coding method.

Referring to FIG. 21, the number of non-zero coefficients up to acurrent coefficient in the current partial block may be compared withthe number of NZ (S2100). Here, the number of NZ is as shown in theembodiment of FIG. 18, and a detailed description thereof will beomitted.

Based on a comparison result of step S2100, probability information of apartial block coefficient flag for a next coefficient may be changed(S1910). Here, the next coefficient may mean a coefficient to be encodednext to a current coefficient according to an encoding order (or anorder according to a scan type). The probability information may referto a probability table predetermined in an image encoding/decodingdevice, a probability value derived from an image encoding/decodingdevice, a variable for calculating probability, and the like.

For example, in encoding a partial block coefficient flag of a nextcoefficient, when the number of non-zero coefficients up to a currentcoefficient in the current partial block is larger than or equal to thenumber of NZ, for the partial block coefficient flag of the nextcoefficient, probability information on occurrence of “0” andprobability information on occurrence of “1” may be exchanged with eachother. In addition, when the number of non-zero coefficients up to acurrent coefficient is smaller than the number of NZ, for the partialblock coefficient flag of the next coefficient, for the partial blockcoefficient flag of the next partial block, probability information onoccurrence of “0” and probability information on occurrence of “0” maynot be exchanged with each other.

The encoding scheme described above may be performed in units of apartial block or a transform block. For example, the encoding scheme maybe restricted to be performed only until the next coefficient reaches acoefficient having a last encoding order in the transform block or inthe partial block. However, the present invention is not limitedthereto, and the same/similar scheme may be performed when the currentcoefficient and the next coefficient belong to different transformblocks or different partial blocks.

When the partial block coefficient flag is encoded according to theabove-described manner, an image decoding device may decode a partialblock coefficient flag of a current partial block, based on the numberof non-zero coefficients up to a previous coefficient in a currentpartial block.

Specifically, probability information on a partial block coefficientflag of a current coefficient may be changed based on the comparisonresult of the number of non-zero coefficients up to the previouscoefficient and the number of NZ, and the partial block coefficient flagmay be decoded based on the changed probability information.

For example, when the number of non-zero coefficients up to a previouscoefficient is larger than or equal to the number of NZ, for the partialblock coefficient flag of the current coefficient, probabilityinformation on occurrence of “0” and the probability information onoccurrence of “1” may be exchanged each other. In addition, when thenumber of non-zero coefficients up to a previous partial block issmaller than a number of NZ, for the partial block coefficient flag ofthe current coefficient, probability information on occurrence of “0”and the probability information on occurrence of “1” may not beexchanged each other.

In addition, a previous coefficient referred to by the currentcoefficient may be restricted to belong to the same partial block as thecurrent coefficient. However, the present invention is not limitedthereto, and a current coefficient may refer to a coefficient thatbelongs to another partial block or another transform block.

The partial block coefficient flag encoding/decoding method describedabove may be selectively used according to a quantization parameter (QP)related to a transform block.

For example, when a QP of the transform block is larger than apredetermined QP threshold value, the above-described encoding/decodingmethod may be restricted so as not to be used. In addition, when a QP ofthe transform block is smaller than a predetermined QP threshold value,the partial block coefficient flag may be encoded/decoded using at leastone of the encoding/decoding methods described above.

The number of QP threshold values may be one, two, or more. The QPthreshold value may be predetermined in an image encoding device. Forexample, the QP threshold value may correspond to a median value of arange of QPs available in the image encoding/decoding device.Alternatively, the image encoding device may determine an optimal QPthreshold value considering encoding efficiency, and encode the QPthreshold value.

Alternatively, the partial block coefficient flag encoding/decodingmethod may be selectively used depending on a size of a transform block(or a partial block).

For example, when a size of a transform block is larger than or equal toa predetermined threshold size, the partial block coefficient flag maybe encoded/decoded using at least one of the encoding/decoding methodsdescribed above. In addition, when a size of a transform block issmaller than a predetermined threshold size, the above-describedencoding/decoding method may be restricted so as not to be used.

The number of threshold size may be one, two, or more. The thresholdsize may be predetermined in an image encoding device. For example, thethreshold size may represented by a×b, wherein a and b are 2, 4, 8, 16,32, 64 or more, and a and b may be equal to or different from eachother. Alternatively, the image encoding device may determine an optimalthreshold size considering encoding efficiency, and encode the thresholdsize.

FIG. 22 is a diagram illustrating a method of changing probabilityinformation of a partial block coefficient flag based on the number ofnon-zero coefficients in a partial block as an embodiment to which thepresent invention is applied.

Referring to FIG. 22, the number of non-zero coefficients in a currentpartial block may be compared with the number of NZ (S2200). Here, thenumber of NZ is as shown in the embodiment of FIG. 18, and a detaileddescription thereof will be omitted.

Based on a comparison result of step S2200, probability information of apartial block coefficient flag for a next partial block may be changed(S2210). Here, the next partial block may mean a partial block to beencoded next to a current partial block according to an encoding order(or an order according to a scan type). The probability information mayrefer to a probability table predetermined in an image encoding/decodingdevice, a probability value derived from an image encoding/decodingdevice, a variable for calculating probability, and the like.

For example, when the number of non-zero coefficients in the currentpartial block is larger than the number of NZ, probability informationof a partial block coefficient flag of a next partial block may bechanged. The change may mean applying other probability information witha high probability that the partial block coefficient flag is “true”.

In addition, when the number of non-zero coefficients in the currentpartial block is smaller than the number of NZ, probability informationof a partial block coefficient flag of a next partial block may not bechanged. That is, a partial block coefficient flag of the next partialblock may use the probability information on the partial blockcoefficient flag of the current partial block as it is.

The encoding scheme described above may be performed in units of atransform block. For example, the encoding scheme may be restricted tobe performed only until the next partial block reaches a partial blockhaving a last encoding order in the transform block. However, thepresent invention is not limited thereto, and the same/similar schememay be performed when the current partial block and the next partialblock belong to different transform blocks.

An image decoding device may decode a partial block coefficient flag ofa partial block according to a same/similar scheme as theabove-described encoding scheme.

FIG. 23 is a diagram illustrating a method of changing probabilityinformation of a partial block coefficient flag based on the number ofnon-zero coefficients up to a current coefficient as an embodiment towhich the present invention is applied.

Referring to FIG. 23, the number of non-zero coefficients up to acurrent coefficient in the current partial block may be compared withthe number of NZ (S2300). The number of non-zero coefficients up to acurrent coefficient may be calculated according to an encoding order ofcoefficients (or an order according to a scan type). The number of NZ isas shown in the embodiment of FIG. 18, and a detailed descriptionthereof will be omitted.

Based on a comparison result of step S2300, a partial block coefficientflag for a next coefficient may be encoded (S2310). Here, the nextcoefficient may mean a coefficient to be encoded next to a currentcoefficient according to an encoding order (or an order according to ascan type). The probability information may refer to a probability tablepredetermined in an image encoding/decoding device, a probability valuederived from an image encoding/decoding device, a variable forcalculating probability, and the like.

For example, when the number of non-zero coefficients up to the currentcoefficient is larger than or equal to the number of NZ, probabilityinformation of a partial block coefficient flag of a next coefficientmay be changed. The change may mean applying other probabilityinformation with a high probability that the partial block coefficientflag is “true”.

In addition, when the number of non-zero coefficients up to the currentcoefficient is smaller than the number of NZ, probability information ofa partial block coefficient flag of a next coefficient may not bechanged. That is, a partial block coefficient flag of the nextcoefficient may use the probability information on the partial blockcoefficient flag of the current coefficient as it is.

The encoding scheme described above may be performed in units of atransform block or a partial block. For example, the encoding scheme maybe restricted to be performed only until the next coefficient reaches acoefficient having a last encoding order in the transform block or thepartial block. However, the present invention is not limited thereto,and the same/similar scheme may be performed when the currentcoefficient and the next coefficient belong to different transformblocks or different partial blocks.

An image decoding device may change probability information of a partialblock coefficient flag according to a same/similar scheme as theabove-described encoding scheme.

In addition, the above-described change of the probability informationmay be performed in consideration of frequency components of a transformblock. Referring to FIG. 16, AC component region (e.g., partial blocks1620, 1630, 1640) may use probability information with a higherprobability of a partial block coefficient flag that is “false”, and DCcomponent region (e.g., partial block 1610) may use probabilityinformation with a higher probability of a partial block coefficientflag that is “true”.

FIG. 24 is a block diagram illustrating an image encoding deviceaccording to an embodiment of the present invention.

Referring to 24, an image encoding device 2400 may include a picturepartitioning module 2410, prediction modules 2420 and 2425, a transformmodule 2430, a quantization module 2435, a rearrangement module 2460, anentropy encoding module 2465, an inverse quantization module 2440, aninverse transform module 2445, a filter module 2450, and a memory 2455.

The constitutional parts shown in FIG. 24 are independently shown so asto represent characteristic functions different from each other in theimage encoding device, and it does not mean that each constitutionalpart is constituted in a constitutional unit of separated hardware orsoftware. In other words, each constitutional part includes each ofenumerated constitutional parts for convenience, and at least twoconstitutional parts of each constitutional part may be combined to formone constitutional part or one constitutional part may be divided into aplurality of constitutional parts to perform each function. Theembodiment where each constitutional part is combined and the embodimentwhere one constitutional part is divided are also included in the scopeof the present invention, if not departing from the essence of thepresent invention.

Also, some of constituents may not be indispensable constituentsperforming essential functions of the present invention but be optionalconstituents improving only performance thereof. The present inventionmay be implemented by including only the indispensable constitutionalparts for implementing the essence of the present invention except theconstituents used in improving performance. The structure including onlythe indispensable constituents except the optional constituents used inimproving only performance is also included in the scope of the presentinvention.

The picture partitioning module 2410 may partition an input picture intoat least one block. Here, a block may mean a coding unit (CU), aprediction unit (PU), or a transform unit (TU). The partitioning may beperformed based on at least one of a quad tree or a binary tree. A quadtree is a method of partitioning an upper-level block into fourlower-level blocks whose width and height are half of the upper-levelblock. A binary tree is a method of partitioning an upper-level blockinto two lower-level blocks whose width or height is half of theupper-level block. Using the binary tree-based partitioning, a block mayhave a square shape as well as a non-square shape.

Hereinafter, in embodiments of the present invention, a coding unit maybe used as a unit for performing encoding, or may be used as a unit forperforming decoding.

The prediction modules 2420 and 2425 may include an inter-predictionmodule 2420 for performing inter-prediction and an intra-predictionmodule 2425 for performing intra-prediction. Whether to performinter-prediction or intra-prediction for a prediction unit may bedetermined, and specific information (e.g., intra-prediction mode,motion vector, reference picture, etc.) according to each predictionmethod may be determined. Here, a processing unit subjected toprediction may be different from a processing unit for which aprediction method and specific contents are determined. For example, aprediction method, a prediction mode and the like may be determined inunits of prediction unit, and a prediction may be performed in units oftransform unit.

The encoding device may determine an optimal prediction mode for anencoding block by using various schemes such as rate-distortionoptimization (RDO) for a residual block obtained by subtracting a sourceblock from a prediction block. In one example, RDO may be determined bythe following Equation 1.

J(Φ,λ)=D(Φ)+λR(Φ)  [Equation 1]

In the above Equation (1), D represents a deterioration due toquantization, R represents a rate of compressed stream, and J representsthe RD cost. Further, Φ represents an encoding mode, λ represents aLagrangian multiplier. λ may be used as a scale correction coefficientfor matching a unit of error amount and bit amount. In an encodingprocedure, an encoding device may determine a mode with a minimum RDcost value as an optimal mode for an encoding block. Here, an RD-costvalue is calculated considering both a bit rate and an error.

Among intra modes, a DC mode, which is a non-directional prediction mode(or a non-angular prediction mode), may use an average value ofneighboring pixels of a current block. FIG. 26 is a diagram forexplaining an intra-prediction method using a DC mode.

After an average value of neighboring pixels is filled in a predictionblock, a filtering may be performed on pixels located at a boundary ofthe prediction block. In one example, weighted sum filtering withneighboring reference pixels may be applied to pixels located at a leftor top boundary of a prediction block. For example, Equation 2 shows anexample of generating prediction pixels through a DC mode for eachregion. In Equation 2, zones R1, R2, R3 are regions located at anoutermost (i.e., boundary) of a prediction block, and weighted sumfiltering may be applied to pixels included in the region.

$\begin{matrix}{{{DC}\mspace{14mu} {value}} = \frac{\begin{matrix}{{\sum\limits_{x = 0}^{{Wid} - 1}{{R\lbrack x\rbrack}\lbrack {- 1} \rbrack}} + {\sum\limits_{y = 0}^{{Hei} - 1}{{R\lbrack {- 1} \rbrack}\lbrack y\rbrack}} +} \\ ( {( {{Wid} + {Hei}} )1} ) )\end{matrix}}{( {{Wid} + {Hei}} )}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack \\{{ {R\; 1\mspace{14mu} {region}} )\mspace{14mu} {{{Pred}\lbrack 0\rbrack}\lbrack 0\rbrack}} = {( {{{R\lbrack {- 1} \rbrack}\lbrack 0\rbrack} + {2*{DC}\mspace{14mu} {value}} + {{R\lbrack 0\rbrack}\lbrack {- 1} \rbrack} + 2} )2}} & \; \\{{{ {R\; 2\mspace{14mu} {region}} )\mspace{14mu} {{{Pred}\lbrack x\rbrack}\lbrack 0\rbrack}} = {( {{{R\lbrack x\rbrack}\lbrack {- 1} \rbrack} + {3*{DC}\mspace{14mu} {value}} + 2} )2}},{x > 0}} & \; \\{{{ {R\; 3\mspace{14mu} {region}} )\mspace{14mu} {{{Pred}\lbrack 0\rbrack}\lbrack y\rbrack}} = {( {{{R\lbrack 0\rbrack}\lbrack y\rbrack} + {3*{DC}\mspace{14mu} {value}} + 2} )2}},{y > 0}} & \; \\{{{ \mspace{79mu} {R\; 4\mspace{14mu} {region}} )\mspace{14mu} {{{Pred}\lbrack x\rbrack}\lbrack y\rbrack}} = {{DC}\mspace{14mu} {value}}},{x > 0},{y > 0}} & \;\end{matrix}$

In the Equation 2, Wid represents a horizontal length of a predictionblock, and Hei represents a vertical length of a prediction block. x, ymeans a coordinate position of each prediction pixel when a most lefttop position of a prediction block is defined as (0, 0). R denotes aneighboring pixel. For example, when pixel s shown in FIG. 26 is definedas R [−1] [−1], pixel a to pixel i may be represented as R [0] [−1] to R[8] [−1], pixel j to pixel r may be represented as R [−1] [0] to R [−1][8]. In the example shown in FIG. 26, a prediction pixel value Pred maybe calculated for each of regions R1 to R4 according to a weighted sumfiltering method as shown in Equation 2.

A planar mode among a non-directional mode is a method of generating aprediction pixel of a current block by applying linear interpolation toneighboring pixels of the current block by distance. For example, FIG.27 is a diagram for explaining an intra-prediction method using a planarmode.

For example, it is assumed that Pred shown in FIG. 27 is predicted in an8×8 encoding block. In this case, pixel e located at a top side of Predand pixel r pixel located at a left bottom side of Pred may be copied toa most bottom side of Pred, and a vertical prediction value may beobtained by linear interpolation by distance in a vertical direction. Inaddition, pixel n located at a left side of Pred and pixel i located ata right top side of Pred may be copied to a most right side of Pred, anda horizontal prediction value may be obtained by linear interpolation bydistance in a horizontal direction. Then, an average value of thehorizontal and vertical prediction values may be determined as a valueof Pred. Equation 3 is a formula expressing a process of obtaining aprediction value Pred according to a planner mode.

$\begin{matrix}{\Pr_{{{ed}{\lbrack x\rbrack}}{\lbrack y\rbrack}} = \frac{\begin{matrix}{\lbrack {( {{Wid} - 1 - x} )*{{R\lbrack {- 1} \rbrack}\lbrack y\rbrack}} \rbrack + \lbrack {( {x + 1} )*{{R\lbrack{Wid}\rbrack}\lbrack {- 1} \rbrack}} \rbrack +} \\{\lbrack {( {{Hei} - 1 - y} )*{{R\lbrack x\rbrack}\lbrack {- 1} \rbrack}} \rbrack + \lbrack {( {y + 1} )*{{R\lbrack {- 1} \rbrack}\lbrack{Hei}\rbrack}} \rbrack + 1}\end{matrix}}{2}} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

In the Equation 3, Wid represents a horizontal length of a predictionblock, and Hei represents a vertical length of a prediction block. x, ymeans a coordinate position of each prediction pixel when a most lefttop position of a prediction block is defined as (0, 0). R denotes aneighboring pixel. For example, when pixel s shown in FIG. 27 is definedas R [−1] [−1], pixel a to pixel i may be represented as R [0] [−1] to R[8] [−1], pixel j to pixel r may be represented as R [−1] [0] to R [−1][8].

FIG. 28 is a diagram for explaining an intra-prediction method using adirectional prediction mode.

A directional prediction mode (or an angular prediction mode) is amethod of generating at least one or more pixels located in any one of Npredetermined directions among neighboring pixels of a current block asprediction samples.

A directional prediction mode may include a horizontal direction modeand a vertical direction mode. Here, a horizontal directional mode meansmodes having greater horizontal directionality than an angularprediction mode directed to 45 degrees to a left top side, and avertical directional mode means modes having greater vertical directionthan an angular prediction mode directed to 45 degrees to a left topside. A directional prediction mode having a prediction directiondirected to 45 degrees to a left top side may be treated as a horizontaldirectional mode or may be treated as a vertical directional mode. InFIG. 28, horizontal directional modes and vertical directional modes areshown.

Referring to FIG. 28, there may be a direction that does not match to aninteger pixel portion for each direction. In such a case, after applyingan interpolation by distance such as a linear interpolation method, aDCT-IF method, a cubic convolution interpolation method, and the like toa distance between a pixel and a neighboring pixel, and the pixel valuesmay be filled in a pixel position matching to a direction of aprediction block.

A residual value (residual block or transform block) between thegenerated prediction block and an original block may be input to thetransform module 2430. A residual block is a minimum unit for transformand quantization procedure. A partitioning method of an encoding blockmay be applied to a transform block. In one example, a transform blockmay be partitioned into four or two partial blocks.

Prediction mode information, motion vector information and the like usedfor prediction may be encoded with a residual value by the entropyencoding module 2465 and may be transmitted to a decoding device. When aparticular encoding mode is used, it is possible to transmit to adecoding device by encoding the original block as it is withoutgenerating the prediction block through the prediction modules 2420 and2425.

The inter-prediction module 2420 may predict the prediction unit basedon information of at least one of a previous picture or a subsequentpicture of the current picture, or may predict the prediction unit basedon information of some encoded regions in the current picture, in somecases. The inter-prediction module 2420 may include a reference pictureinterpolation module, a motion prediction module, and a motioncompensation module.

The reference picture interpolation module may receive reference pictureinformation from the memory 2455 and may generate pixel information ofan integer pixel or less than the integer pixel from the referencepicture. In the case of luma pixels, an 8-tap DCT-based interpolationfilter having different filter coefficients may be used to generatepixel information of an integer pixel or less than an integer pixel inunits of a ¼ pixel. In the case of chroma signals, a 4-tap DCT-basedinterpolation filter having different filter coefficient may be used togenerate pixel information of an integer pixel or less than an integerpixel in units of a ⅛ pixel.

The motion prediction module may perform motion prediction based on areference picture interpolated by the reference picture interpolationmodule. As methods for calculating a motion vector, various methods,such as a full search-based block matching algorithm (FBMA), a threestep search (TSS), a new three-step search algorithm (NTS), etc., may beused. The motion vector may have a motion vector value in units of a ½pixel or a ¼ pixel based on an interpolated pixel. The motion predictionmodule may predict a current prediction unit by changing the motionprediction method. As motion prediction methods, various methods, suchas a skip method, a merge method, an Advanced Motion Vector Prediction(AMVP) method, etc., may be used.

An encoding device may generate motion information of a current blockbased on motion estimation or motion information of a neighboring block.Here, the motion information may include at least one of a motionvector, a reference image index and a prediction direction.

The intra prediction module 2425 may generate a prediction unit based onreference pixel information neighboring to a current block which ispixel information in the current picture. When the neighboring block ofthe current prediction unit is a block subjected to inter-prediction andthus a reference pixel is a pixel subjected to inter-prediction, thereference pixel included in the block subjected to inter-prediction maybe replaced with reference pixel information of a neighboring blocksubjected to intra-prediction. That is, when a reference pixel is notavailable, at least one reference pixel of available reference pixelsmay be used instead of unavailable reference pixel information.

Prediction modes in intra-prediction may include a directionalprediction mode using reference pixel information depending on aprediction direction and a non-directional prediction mode not usingdirectional information in performing prediction. A mode for predictingluma information may be different from a mode for predicting chromainformation, and in order to predict the chroma information,intra-prediction mode information used to predict luma information orpredicted luma signal information may be utilized.

In the intra-prediction method, a prediction block may be generatedafter applying an Adaptive Intra Smoothing (AIS) filter to a referencepixel depending on the prediction modes. The type of the AIS filterapplied to the reference pixel may vary. In order to perform the intraprediction method, an intra prediction mode of the current predictionunit may be predicted from the intra prediction mode of the predictionunit neighboring to the current prediction unit. In prediction of theprediction mode of the current prediction unit by using mode informationpredicted from the neighboring prediction unit, when the intraprediction mode of the current prediction unit is the same as the intraprediction mode of the neighboring prediction unit, informationindicating that the prediction modes of the current prediction unit andthe neighboring prediction unit are equal to each other may betransmitted using predetermined flag information, and when theprediction mode of the current prediction unit is different from theprediction mode of the neighboring prediction unit, entropy encoding maybe performed to encode prediction mode information of the current block.

Also, a residual block including information on a residual value whichis a difference between the prediction unit subjected to prediction andthe original block of the prediction unit may be generated based onprediction units generated by the prediction modules 2420 and 2425. Thegenerated residual block may be input to the transform module 2430.

The transform module 2430 may transform the residual block includingresidual data using a transform method, such as discrete cosinetransform (DCT), discrete sine transform (DST), and Karhunen LoeveTransform (KLT). In order to make easy use of a transform method, amatrix operation is performed using a basis vector. Here, depending on aprediction mode in which a prediction block is encoded, varioustransform methods may be variously mixed and used in matrix operation.For example, when performing intra-prediction, depending onintra-prediction mode, discrete cosine transform may be used forhorizontal direction and discrete sine transform may be used forvertical direction.

The quantization module 2435 may quantize values transformed to afrequency domain by the transform module 2430. That is, the quantizationmodule 2435 may quantize transform coefficients of a transform blockgenerated from the transform module 2430, and generate a quantizedtransform block having the quantized transform coefficients. Here, thequantization methods may include Dead Zone Uniform ThresholdQuantization (DZUTQ) or a Quantization Weighted Matrix, and the like. Itis also possible to use an improved quantization methods that improvesthese quantization methods. The quantization coefficients may varydepending on a block or an importance of an image. Values calculated bythe quantization module 2435 may be provided to the inverse quantizationmodule 2440 and the rearrangement module 2460.

The transform module unit 2430 and/or the quantization module 2435 maybe selectively included in the image encoding device 2400. That is, theimage encoding device 2400 may perform at least one of transformation orquantization on the residual data of the residual block, or may skipboth the transformation and the quantization, thereby encoding theresidual block. A block provided as an input of the entropy encodingmodule 2465 is generally referred to as a transform block (or quantizedtransform block) even though either the transformation or thequantization is not performed or both the transformation and thequantization are not performed in the image encoding device 2400.

The rearrangement module 2460 may rearrange coefficients of quantizedresidual values.

The rearrangement module 2460 may change a coefficient in the form of atwo-dimensional block into a coefficient in the form of aone-dimensional vector through a coefficient scanning method. Forexample, the rearrangement module 2460 may scan from a DC coefficient toa coefficient in a high frequency domain using a predetermined scanningmethod so as to change the coefficients to be in the form ofone-dimensional vectors.

The entropy encoding module 2465 may perform entropy encoding based onthe values calculated by the rearrangement module 2460. Entropy encodingmay use various encoding methods, for example, exponential Golombcoding, context-adaptive variable length coding (CAVLC), andcontext-adaptive binary arithmetic coding (CABAC).

The entropy encoding module 2465 may encode various information, such asresidual value coefficient information and block type information of thecoding unit, prediction mode information, partition unit information,prediction unit information and transmit unit information, motion vectorinformation, reference frame information, interpolation information of ablock, filtering information, etc. from the rearrangement module 2460and the prediction modules 2420 and 2425. In the entropy encoding module2465, the coefficient of the transform block may be encoded, in units ofpartial block in a transform block, as a non-zero coefficient, acoefficient whose absolute value is larger than 1 or 2, and varioustypes of flags indicating a sign of a coefficient, etc. The coefficientthat is not encoded with only the flag may be encoded through theabsolute value of the difference between the coefficient encoded throughthe flag and the coefficient of the actual transform block.

The entropy encoding module 2465 may entropy encode coefficients of thecoding unit input from the rearrangement module 2460.

The inverse quantization module 2440 may inversely quantize the valuesquantized by the quantization module 2435 and the inverse transformmodule 2445 may inversely transform the values transformed by thetransform module 2430.

In addition, the inverse quantization module 2440 and the inversetransform module 2445 may perform inverse quantization and inversetransformation by inversely using the quantization method and thetransformation method used in the quantization module 2435 and thetransform module 2430. In addition, when the transform module 2430 andthe quantization module 2435 perform only quantization and do notperform the transformation, only the inverse quantization is performedand the inverse transformation may not be performed. When both thetransformation and the quantization are not performed, the inversequantization module 2440 and the inverse transform module 2445 mayneither perform inverse transform nor inverse quantization nor beincluded in the image encoding device 2400 and may be omitted.

The residual value generated by the inverse quantization module 2440 andthe inverse transform module 2445 may be combined with the predictionunit predicted by a motion estimation module, a motion compensationmodule, and the intra-prediction module included in the predictionmodules 2420 and 2425 so as to generate a reconstructed block.

The filter module 2450 may include at least one of a deblocking filter,an offset correction unit, and an adaptive loop filter (ALF).

The deblocking filter may remove block distortion that occurs due toboundaries between the blocks in the reconstructed picture. In order todetermine whether to perform deblocking, the pixels included in severalrows or columns included in the block may be a basis of determiningwhether to apply the deblocking filter to the current block. When thedeblocking filter is applied to the block, a strong filter or a weakfilter may be applied depending on required deblocking filteringstrength. Also, in applying the deblocking filter, horizontal directionfiltering and vertical direction filtering may be processed in parallel.

The offset correction module may correct offset with the originalpicture in units of a pixel in the picture subjected to deblocking. Inorder to perform the offset correction on a particular picture, it ispossible to use a method of applying offset in consideration of edgeinformation of each pixel or a method of partitioning pixels of apicture into the predetermined number of regions, determining a regionto be subjected to perform offset, and applying the offset to thedetermined region.

Adaptive loop filtering (ALF) may be performed based on the valueobtained by comparing the filtered reconstructed picture and theoriginal picture. The pixels included in the picture may be divided intopredetermined groups, a filter to be applied to each of the groups maybe determined, and filtering may be individually performed for eachgroup. Information on whether to apply ALF and a luma signal may betransmitted by coding units (CU), and the shape and filter coefficientof a filter for ALF may vary depending on each block. Also, the filterfor ALF in the same shape (fixed shape) may be applied regardless ofcharacteristics of the application target block.

The memory 2455 may store the reconstructed block or picture calculatedthrough the filter module 2450, and the stored reconstructed block orpicture may be provided to the prediction modules 2420 and 2425 inperforming inter-prediction.

FIG. 25 is a block diagram illustrating an image decoding deviceaccording to an embodiment of the present invention.

Referring to FIG. 25, the image decoding device 2500 may include anentropy decoding module 2510, a rearrangement module 2515, an inversequantization module 2520, an inverse transform module 2525, predictionmodules 2530 and 2535, a filter module 2540, and a memory 2545.

When an image bitstream is input from the image encoding device, theinput bitstream may be decoded according to an inverse process of theimage encoding device.

The entropy decoding module 2510 may perform entropy decoding accordingto an inverse process of entropy encoding by the entropy encoding moduleof the image encoding device. For example, corresponding to the methodsperformed by the image encoding device, various methods, such asexponential Golomb coding, context-adaptive variable length coding(CAVLC), and context-adaptive binary arithmetic coding (CABAC) may beapplied. In the entropy decoding module 2510, the coefficient of thetransform block may be decoded, in units of partial block in a transformblock, based on a non-zero coefficient, a coefficient whose absolutevalue is larger than 1 or 2, and various types of flags indicating asign of a coefficient, etc. The coefficient that is not represented byonly the flag may be decoded through combination of coefficientrepresented by the flag and coefficient that is signaled.

The entropy decoding module 2510 may decode information onintra-prediction and inter-prediction performed by the image encodingdevice.

The rearrangement module 2515 may perform rearrangement on the bitstreamentropy decoded by the entropy decoding module 2510 based on therearrangement method used in the image encoding device. Therearrangement may include reconstructing and rearranging thecoefficients in the form of one-dimensional vectors to the coefficientin the form of two-dimensional blocks. The rearrangement module 2515 mayreceive information related to coefficient scanning performed in theimage encoding device and may perform rearrangement via a method ofinversely scanning the coefficients based on the scanning orderperformed in the image encoding device.

The inverse quantization module 2520 may perform inverse quantizationbased on a quantization parameter received from the image encodingdevice and the rearranged coefficients of the block.

The inverse transform module 2525 may perform the inverse transform ofthe inverse quantized transform coefficients according to apredetermined transform method. Here, the transform method may bedetermined based on a prediction method (inter/intra-prediction), asize/shape of a block, information on intra-prediction mode, etc.

The prediction modules 2530 and 2535 may generate a prediction blockbased on information on prediction block generation received from theentropy decoding module 2510 and previously decoded block or pictureinformation received from the memory 2545.

The prediction modules 2530 and 2535 may include a prediction unitdetermination module, an inter-prediction module, and anintra-prediction module. The prediction unit determination module mayreceive various information, such as prediction unit information,prediction mode information of an intra-prediction method, informationon motion prediction of an inter-prediction method, etc. from theentropy decoding module 2510, may divide a current coding unit intoprediction units, and may determine whether inter-prediction orintra-prediction is performed on the prediction unit. By usinginformation required in inter-prediction of the current prediction unitreceived from the image encoding device, the inter-prediction module2530 may perform inter-prediction on the current prediction unit basedon information of at least one of a previous picture or a subsequentpicture of the current picture including the current prediction unit.Alternatively, inter-prediction may be performed based on information ofsome pre-reconstructed regions in the current picture including thecurrent prediction unit.

In order to perform inter-prediction, it may be determined for thecoding unit which of a skip mode, a merge mode, an AMVP mode, and aninter block copy mode is used as the motion prediction method of theprediction unit included in the coding unit.

The intra-prediction module 2535 may generate a prediction block basedon pixel information in the current picture. When the prediction unit isa prediction unit subjected to intra-prediction, intra-prediction may beperformed based on intra-prediction mode information of the predictionunit received from the image encoding device. The intra-predictionmodule 2535 may include an adaptive intra smoothing (AIS) filter, areference pixel interpolation module, a DC filter. The AIS filterperforms filtering on the reference pixel of the current block, andwhether to apply the filter may be determined depending on theprediction mode of the current prediction unit. AIS filtering may beperformed on the reference pixel of the current block by using theprediction mode of the prediction unit and AIS filter informationreceived from the image encoding device. When the prediction mode of thecurrent block is a mode where AIS filtering is not performed, the AISfilter may not be applied.

When the prediction mode of the prediction unit is a prediction mode inwhich intra-prediction is performed based on the pixel value obtained byinterpolating the reference pixel, the reference pixel interpolationmodule may interpolate the reference pixel to generate the referencepixel of an integer pixel or less than an integer pixel. When theprediction mode of the current prediction unit is a prediction mode inwhich a prediction block is generated without interpolation thereference pixel, the reference pixel may not be interpolated. The DCfilter may generate a prediction block through filtering when theprediction mode of the current block is a DC mode.

The reconstructed block or picture may be provided to the filter module2540. The filter module 2540 may include the deblocking filter, theoffset correction module, the ALF.

Information on whether or not the deblocking filter is applied to thecorresponding block or picture and information on which of a strongfilter and a weak filter is applied when the deblocking filter isapplied may be received from the image encoding device. The deblockingfilter of the image decoding device may receive information on thedeblocking filter from the image encoding device, and may performdeblocking filtering on the corresponding block.

The offset correction module may perform offset correction on thereconstructed picture based on the type of offset correction and offsetvalue information applied to a picture in performing encoding.

The ALF may be applied to the coding unit based on information onwhether to apply the ALF, ALF coefficient information, etc. receivedfrom the image encoding device. The ALF information may be provided asbeing included in a particular parameter set.

The memory 2545 may store the reconstructed picture or block for use asa reference picture or block, and may provide the reconstructed pictureto an output module.

An encoding block may be partitioned into at least one block.Specifically, here, the encoding block may be partitioned into from amaximum-size encoding block to a minimum-size encoding block based onquad tree partitioning or a binary tree partitioning (or dual treepartitioning). Information on a maximum size encoding block and aminimum size encoding block, or information on a difference valuebetween a maximum size encoding block and a minimum size encoding blockmay be signaled to a decoding device through a bitstream.

Quad tree (QT) partitioning is a method of partitioning an encodingblock into four blocks. By the QT partitioning, an encoding block may bepartitioned into four blocks whose vertical length and horizontal lengthare reduced to ½. A maximum size or a minimum size of encoding blockcapable of QT partitioning, the number of QT partitioning (or a maximumpartitioning depth), a partitioning depth of a minimum size block, adepth capable of partitioning from a maximum size encoding block capableof QT partitioning, and the like may be signaled via an upper header.Here, the upper header may include a slice layer, a picture layer, asequence layer, a video layer, or the like.

Binary tree (BT) partitioning is a method of partitioning an encodingblock into two blocks. By BT partitioning, an encoded block may bedivided into two blocks in the horizontal or vertical direction. Forexample, by BT partitioning, an encoding block may be partitioned intotwo blocks vertical length and horizontal length are reduced to ½, ortwo blocks whose vertical length or horizontal length is reduced to ¾ or¼, respectively. Accordingly, BT partitioning may mean a method ofpartitioning an encoding block with a degree of precision of 1/N (N≥≥2).A maximum size or a minimum size of an encoding block capable of BTpartitioning, the number of B partitioning (or a maximum partitioningdepth), a partitioning depth of a minimum size block, a depth capable ofpartitioning from a maximum size encoding block capable of BTpartitioning, or the like may be signaled via an upper header.

Hereinafter, QT partitioning and BT partitioning will be described indetail with reference to drawings.

FIG. 29 is a diagram illustrating a method of encoding QT partitioninginformation for an encoding block. In the present embodiment, a‘current’ encoding block represents a block subjected to encoding at aspecific time point. For example, a current encoding block may refer toa block having a partitioning depth at which encoding is currentlyperformed. For example, when an encoding block is input for encoding, afirst input encoding block may be treated as a ‘current encoding block’.Thereafter, as the encoding block is partitioned, when encoding isperformed for a partitioned block, the partitioned block may be treatedas a ‘current encoding block’.

When an encoding block is input, the input encoding block may be treatedas a ‘current encoding block’ (S2901). The encoding block that is inputfirst may refer to an encoding block having a highest level partitioningdepth to be encoded (i.e., an encoding block having a depth of 0).

An encoding device may encode QT partitioning information for a currentencoding block (S2902). Here, the QT partitioning information indicateswhether or not QT partitioning has performed for a current encodingblock. When a current encoding block is QT partitioned, QT partitioninginformation may be set to ‘true’, and when a current encoding block isnot QT partitioned, QT partitioning information may be set to ‘false’.

When it is determined that a current encoding block is not QTpartitioned (S2903), QT partitioning procedure for the current encodingblock may be terminated. In addition, when it is determined that acurrent encoding block is QT partitioned (S2903), four partial blocks(or sub-blocks) included in the current encoding block may be generatedthrough QT partitioning (S2904).

When a current encoding block is partitioned into four partial blocks,according to an encoding order, one of the partial blocks included inthe current encoding block is set as a current partial block, and QTpartitioning information of the current partial block may be encoded(S2905). Here, the encoding order between the partial blocks may followraster scan, Z scan, or the like, or may follow a predetermined order.That is, according to an encoding order of partial blocks, QTpartitioning information of partial blocks may be sequentially encoded.

When it is determined that a current partial block is not QT partitioned(S2906), the QT partitioning procedure may be terminated based onwhether the current partial block is a last block in the currentencoding block and in the input encoding block (S2907, S2908). Forexample, when a current partial block is not QT partitioned, and thecurrent partial block is a last block in the current encoding block andin the input encoding block, the QT partitioning procedure may beterminated. In addition, when a current partial block is not the lastpartial block of the current encoding block, or when the currentencoding block is the last partial block of the current encoding blockbut not the last partial block in the input encoding block, QTpartitioning information encoding procedure may be performed for a nextpartial block as a current partial block (S2909).

In addition, when it is determined that a current partial block is QTpartitioned (S2906), the current partial block may be set as the currentencoding block (S2910), and the newly set current encoding block may bepartitioned into four partial blocks (S2904). When the newly set currentencoding block is partitioned into four partial blocks, QT partitioninginformation encoding procedure for the four newly generated partialblocks may be repeatedly performed (S2905 to S2910).

An encoding device may encode a maximum size of an encoding blockcapable of QT partitioning, a depth of an encoding block capable of QTpartitioning and the like, through an upper header, based on thepartitioning result of the current encoding block.

The partitioning result of the current encoding block may be used todetermine a maximum size of an encoding block capable of QTpartitioning, a depth of an encoding block capable of QT partitioningand the like, for a next encoding block.

FIG. 30 is a diagram illustrating a method of encoding BT partitioninginformation for an encoding block.

When an encoding block is input, the input encoding block may be treatedas a current encoding block (S3001). The encoding block that is inputfirst may refer to an encoding block having a highest level partitioningdepth to be encoded (i.e., an encoding block having a depth of 0).

An encoding device may encode BT partitioning information for a currentencoding block (S3002). Here, the BT partitioning information indicateswhether or not BT partitioning has performed for a current encodingblock. When a current encoding block is BT partitioned, BT partitioninginformation may be set to ‘true’, and when a current encoding block isnot BT partitioned, BT partitioning information may be set to ‘false’.

When a current encoding block is partitioned into two partial blocks, anencoding device may further encode information on a partitioningpattern. In one example, the information on the partitioning pattern mayfurther include information on at least one of a partitioning directionor a degree of precision. Here, the partitioning direction indicateswhether a current encoding block is partitioned in a horizontaldirection or a vertical direction. In addition, a degree of precision ofa current block may be used as an element for determining a size of apartial block. For example, according to a degree of precision of acurrent block, it may be partitioned into two partial blocks having ahorizontal length or a vertical length of ¼ and ¾, respectively,compared to an upper level block, or it may be partitioned into twopartial blocks having a horizontal length or a vertical length of ½,respectively, compared to an upper level block.

For an additional example, the information on the partitioning patternmay include a partitioning index. Here, the partitioning index indicatesa partitioning shape of a current encoding block. For example, accordingto a degree of precision, a current encoding block may be partitionedinto partial blocks having a horizontal length of ¼ compared to an upperlevel block, a horizontal length of ½ compared to an upper level block,a horizontal length of ¾ compared to an upper level block, a verticallength of ¼ compared to an upper level block, a vertical length of ½compared to an upper level block, a vertical length of ¾ compared to anupper level block, or the like. Accordingly, an encoding device maydetermine which of the seven cases the partitioning pattern of a currentdecoding block corresponds to, and then may encode an indexcorresponding to the partitioning pattern of the current decoding blockaccording to the determination result.

When it is determined that a current encoding block is not BTpartitioned (S3003), BT partitioning procedure for the current encodingblock may be terminated. In addition, when it is determined that acurrent encoding block is BT partitioned (S3003), two partial blocks (orsub-blocks) included in the current encoding block may be generatedthrough BT partitioning (S3004).

When a current encoding block is partitioned into two partial blocks,according to an encoding order, one of the partial blocks included inthe current encoding block is set as a current partial block, and BTpartitioning information of the current partial block may be encoded(S3005). Here, the encoding order between the partial blocks may followraster scan, Z scan, or the like, or may follow a predetermined order.That is, according to an encoding order of partial blocks, BTpartitioning information of partial blocks may be sequentially encoded.

When it is determined that a current partial block is not BT partitioned(S3006), the BT partitioning procedure may be terminated based onwhether the current partial block is a last block in the currentencoding block and in the input encoding block (S3007, S3008). Forexample, when a current partial block is not BT partitioned, and thecurrent partial block is a last block in the current encoding block andin the input encoding block, the BT partitioning procedure may beterminated. In addition, when a current partial block is not the lastpartial block of the current encoding block, or when the currentencoding block is the last partial block of the current encoding blockbut not the last partial block in the input encoding block, BTpartitioning information encoding procedure may be performed for a nextpartial block as a current partial block (S3009).

In addition, when it is determined that a current partial block is BTpartitioned (S3006), the current partial block may be set as the currentencoding block (S3010), and the newly set current encoding block may bepartitioned into two partial blocks (S3004). When the newly set currentencoding block is partitioned into two partial blocks, BT partitioninginformation encoding procedure for the two newly generated partialblocks may be repeatedly performed (S3005 to S3010).

An encoding device may encode a maximum size of an encoding blockcapable of BT partitioning, a depth of an encoding block capable of BTpartitioning and the like, through an upper header, based on thepartitioning result of the current encoding block.

The partitioning result of the current encoding block may be used todetermine a maximum size of an encoding block capable of BTpartitioning, a depth of an encoding block capable of BT partitioningand the like, for a next encoding block.

FIG. 31 is a diagram illustrating a method of decoding QT partitioninginformation for a decoding block. In the present embodiment, a ‘current’decoding block represents a block subjected to decoding at a specifictime point. For example, a current decoding block may refer to a blockhaving a partitioning depth at which decoding is currently performed.For example, when a decoding block is input for decoding, a first inputdecoding block may be treated as a ‘current decoding block’. Thereafter,as the decoding block is partitioned, when decoding is performed for apartitioned block, the partitioned block may be treated as a ‘currentdecoding block’.

When a decoding block is input, the input decoding block may be treatedas a ‘current decoding block’ (S3101). The decoding block that is inputfirst may refer to a decoding block having a highest level partitioningdepth to be decoded (i.e., a decoding block having a depth of 0).

A decoding device may decode QT partitioning information for a currentdecoding block (S3102). Here, the QT partitioning information indicateswhether or not QT partitioning has performed for a current decodingblock. When QT partitioning information is ‘true’, a current decodingblock may QT partitioned, and when QT partitioning information is‘false’, a current decoding block may not be QT partitioned.

When QT partitioning information is false, that is, when it isdetermined that a current decoding block is not QT partitioned (S3103),QT partitioning procedure for the current decoding block may beterminated. In addition, when QT partitioning information is true, thatis, when it is determined that a current decoding block is QTpartitioned (S3103), four partial blocks (or sub-blocks) included in thecurrent decoding block may be generated through QT partitioning (S3004).

When a current decoding block is partitioned into four partial blocks,according to an decoding order, one of the partial blocks included inthe current decoding block is set as a current partial block, and QTpartitioning information of the current partial block may be decoded(S3105). Here, the decoding order between the partial blocks may followraster scan, Z scan, or the like, or may follow a predetermined order.That is, according to a decoding order of partial blocks, QTpartitioning information of partial blocks may be sequentially decoded.

When QT partitioning information of a current partial block is false,that is, when it is determined that a current partial block is not QTpartitioned (S3106), the QT partitioning procedure may be terminatedbased on whether the current partial block is a last block in thecurrent decoding block and in the input decoding block (S3107, S3108).For example, when a current partial block is not QT partitioned, and thecurrent partial block is a last block in the current decoding block andin the input decoding block, the QT partitioning procedure may beterminated. In addition, when a current partial block is not the lastpartial block of the current decoding block, or when the currentdecoding block is the last partial block of the current decoding blockbut not the last partial block in the input decoding block, QTpartitioning information decoding procedure may be performed for a nextpartial block as a current partial block (S3109).

In addition, when QT partitioning information of a current partial blockis true, that is, when it is determined that a current partial block isQT partitioned (S3106), the current partial block may be set as thecurrent decoding block (S3110), and the newly set current decoding blockmay be partitioned into four partial blocks (S3104). When the newly setcurrent decoding block is partitioned into four partial blocks, QTpartitioning information decoding procedure for the four newly generatedpartial blocks may be repeatedly performed (S3105 to S3110).

In the above-described embodiment, when a size of the current decodingblock is equal to or smaller than a maximum block size capable of QTpartitioning signaled from an upper header, or a depth of the currentdecoding block is equal to or greater than a maximum block size capableof QT partitioning signaled from an upper header, decoding of thepartitioning information for the current decoding block may be omittedand the QT partitioning may not be performed for the current decodingblock anymore.

FIG. 32 is a diagram illustrating a method of decoding BT partitioninginformation for a decoding block.

When a decoding block is input, the input decoding block may be treatedas a current decoding block (S3201). The decoding block that is inputfirst may refer to a decoding block having a highest level partitioningdepth to be decoded (i.e., a decoding block having a depth of 0).

A decoding device may decode BT partitioning information for a currentdecoding block (S3202). Here, the BT partitioning information indicateswhether or not BT partitioning has performed for a current decodingblock. When BT partitioning information is ‘true’, a current decodingblock may be BT partitioned, BT partitioning information may be set to‘true’, and when BT partitioning information is ‘false’, a currentdecoding block may not be BT partitioned.

When BT partitioning information is true, that is, when a currentdecoding block is BT partitioned, a decoding device may further decodeinformation on a partitioning pattern. In one example, the informationon the partitioning pattern may further include information on at leastone of a partitioning direction or a degree of precision. Here, thepartitioning direction indicates whether a current decoding block ispartitioned in a horizontal direction or a vertical direction. Inaddition, a degree of precision of a current block may be used as anelement for determining a size of a partial block. For example,according to a degree of precision of a current block, it may bepartitioned into two partial blocks having a horizontal length or avertical length of ¼ and ¾, respectively, compared to an upper levelblock, or it may be partitioned into two partial blocks having ahorizontal length or a vertical length of ½, respectively, compared toan upper level block.

For an additional example, the information on the partitioning patternmay include a partitioning index. Here, the partitioning index indicatesa partitioning shape of a current decoding block. For example, accordingto a degree of precision, a current decoding block may be partitionedinto partial blocks having a horizontal length of ¼ compared to an upperlevel block, a horizontal length of ½ compared to an upper level block,a horizontal length of ¾ compared to an upper level block, a verticallength of ¼ compared to an upper level block, a vertical length of ½compared to an upper level block, a vertical length of ¾ compared to anupper level block, or the like. Accordingly, a decoding device maydecode an index indicating one of the seven cases may determine apartitioning pattern of the current decoding block.

When BT partitioning information is false, that is, when it isdetermined that a current decoding block is not BT partitioned (S3203),BT partitioning procedure for the current decoding block may beterminated. In addition, when BT partitioning information is true, thatis, when it is determined that a current decoding block is BTpartitioned (S3203), two partial blocks (or sub-blocks) included in thecurrent decoding block may be generated through BT partitioning (S3204).

When a current decoding block is partitioned into two partial blocks,according to an decoding order, one of the partial blocks included inthe current decoding block is set as a current partial block, and BTpartitioning information of the current partial block may be decoded(S3205). Here, the decoding order between the partial blocks may followraster scan, Z scan, or the like, or may follow a predetermined order.That is, according to a decoding order of partial blocks, BTpartitioning information of partial blocks may be sequentially decoded.

When it is determined that a current partial block is not BT partitioned(S3206), the BT partitioning procedure may be terminated based onwhether the current partial block is a last block in the currentdecoding block and in the input decoding block (S3207, S3208). Forexample, when a current partial block is not BT partitioned, and thecurrent partial block is a last block in the current decoding block andin the input decoding block, the BT partitioning procedure may beterminated. In addition, when a current partial block is not the lastpartial block of the current decoding block, or when the currentdecoding block is the last partial block of the current decoding blockbut not the last partial block in the input decoding block, BTpartitioning information decoding procedure may be performed for a nextpartial block as a current partial block (S3209).

In addition, when it is determined that a current partial block is BTpartitioned (S3206), the current partial block may be set as the currentdecoding block (S3210), and the newly set current decoding block may bepartitioned into two partial blocks (S3204). When the newly set currentdecoding block is partitioned into two partial blocks, BT partitioninginformation decoding procedure for the two newly generated partialblocks may be repeatedly performed (S3205 to S3210).

In the above-described embodiment, when a size of the current decodingblock is equal to or smaller than a maximum block size capable of BTpartitioning signaled from an upper header, or a depth of the currentdecoding block is equal to or greater than a maximum block size capableof QT partitioning signaled from an upper header, decoding of thepartitioning information for the current decoding block may be omittedand the BT partitioning may not be performed for the current decodingblock anymore.

In the examples shown in FIG. 29 to FIG. 32, a method of recursivelypartitioning an encoding/decoding block of a maximum size using QTpartitioning or BT partitioning has been described. Here, inpartitioning an encoding/decoding block into a plurality of partialblocks, QT partitioning method and BT partitioning method may be used incombination, and an order of QT partitioning and BT partitioning may bevariously set. For example, an encoding device may proceed withpartitioning a maximum encoding block using QT partitioning, and when apartial block determined to be optimal for applying BT partitioning isfound, may terminate QT partitioning and may proceed with partitioningthe partial block through the BT partitioning. Alternatively, when apartial block generated from BT partitioning is determined to be optimalfor applying QT partitioning, the partial block may be partitioned usingQT partitioning. As such, an encoding device may identify an optimalpartitioning method for each block, and accordingly may encodeinformation indicating optimal partitioning method for each block.

For additional example, a decoding device may decode QT partitioninginformation or BT partitioning information to determine an optimalpartitioning state of a decoding block. Here, either QT partitioningmethod or BT partitioning method may be applied only when the othermethod may not be applied. For example, BT partitioning information fora predetermined block may be decoded only when QT division informationfor the predetermined block is false or when an upper level blockincluding the predetermined block is BT partitioned.

In encoding block partitioning information, an encoding device mayencode information indicating whether each partitioning method is usedthrough an upper header. For example, encoding device may encode,through an upper header, information indicating whether QT partitioningis used, whether BT partitioning is used, or the like. For example, whenit is determined that QT partitioning is used but BT partitioning is notused, an encoding block may be partitioned using only QT partitioning.In this case, encoding for BT partitioning information indicatingwhether an encoding block has been BT partitioned may be omitted. Foradditional example, when it is determined that both QT partitioning andBT partitioning are to be used, an encoding block may be partitionedusing QT and BT partitioning modes.

FIG. 33 is a diagram illustrating a state of partitioning in an encodingblock.

For convenience of explanation, it is assumed that, when a block is BTpartitioned, partial blocks generated by BT partitioning may not bepartitioned into BT blocks any more. In the example shown in FIG. 33, asolid line indicates that it is partitioned using QT partitioningmethod, and a dotted line indicates that it is partitioned using BTpartitioning method. Referring to FIG. 33, it is shown that a subblockhaving a width and a length reduced by ½ of an upper level block isgenerated by QT partitioning, and a subblock in which one of ahorizontal or vertical length is reduced to ½ of an upper level block ora subblock in which one of a horizontal or vertical length is reduced to¼ of an upper level block is generated by BT partitioning. Accordingly,in the illustrated example, a maximum degree of precision ofpartitioning of an encoding block may be ¼. Numbers indicated on eachpartitioning line indicate a partitioning order.

Referring to FIG. 33, a partitioning line {circle around (1)} indicatesthat QT partitioning is optimal for a first input encoding block. Apartitioning line {circle around (2)} indicates that BT horizontal ½partitioning is an optimal partitioning for a left top partial blockpartitioned by the partitioning line {circle around (1)}. A partitioningline {circle around (3)} is indicates that BT vertical ½ partitioning isan optimal partitioning for a top partial block partitioned by thepartitioning line {circle around (2)}. A partitioning line {circlearound (4)} indicates that BT horizontal ½ partitioning is an optimalpartitioning for a bottom partial block partitioned by the partitioningline {circle around (2)}. A partitioning line {circle around (5)}indicates that BT vertical ½ partitioning is an optimal partitioning fora right top partial block partitioned by the partitioning line {circlearound (1)}. A partitioning line {circle around (6)} indicates that BTvertical ½ partitioning is an optimal partitioning for a left partialblock partitioned by the partitioning line {circle around (5)}. Apartitioning line {circle around (7)} indicates that BT vertical ½partitioning is an optimal partitioning for a right partial blockpartitioned by the partitioning line {circle around (5)}. A partitioningline {circle around (8)} indicates that QT partitioning is an optimalpartitioning for a left bottom partial block partitioned by thepartitioning line {circle around (1)}. A partitioning line {circlearound (9)} indicates that BT horizontal ½ partitioning is an optimalpartitioning for a left top partial block partitioned by thepartitioning line {circle around (8)}. A partitioning line {circlearound (10)} indicates that BT horizontal ¾ partitioning is an optimalpartitioning for a bottom partial block partitioned by the partitioningline {circle around (9)}. A partitioning line {circle around (11)}indicates that BT horizontal ¼ partitioning is an optimal partitioningfor a left bottom partial block partitioned by the partitioning line{circle around (8)}. A partitioning line {circle around (12)} indicatesthat BT horizontal ½ partitioning is an optimal partitioning for a rightbottom partial block partitioned by the partitioning line {circle around(1)}. A partitioning line {circle around (13)} indicates that BTvertical ¾ partitioning is an optimal partitioning for a top partialblock partitioned by the partitioning line {circle around (12)}. Apartitioning line {circle around (14)} indicates that BT vertical ½partitioning is an optimal partitioning for a bottom partial blockpartitioned by the partitioning line {circle around (12)}. Apartitioning line {circle around (15)} indicates that BT vertical ¾partitioning is an optimal partitioning for a right partial blockpartitioned by the partitioning line {circle around (14)}.

FIG. 34 is a diagram illustrating an optimal partitioning state of aninput encoding block shown in FIG. 33 using a tree structure.

In case of QT partitioning, since there are two cases, that is, a casewhere the QT partitioning is not performed and a case where the block ispartitioned into four partial blocks (i.e., partitioning horizontal andvertical by ½) according to the QT partitioning, QT partitioninginformation may be represented as 0 or 1. Cases for BT partitioning mayinclude a case where BT partitioning is not performed and a case where ablock is partitioned into two partial blocks according to the BTpartitioning may be included. Here, when a block is partitioned into twopartial blocks, depending on a degree of precision, there are variouscases where a block is partitioned into partial blocks having ahorizontal length of ¼ of an upper level block, where a block ispartitioned into partial blocks having a horizontal length of ½ of anupper level block, where a block is partitioned into partial blockshaving a horizontal length of ¾ of an upper level block, where a blockis partitioned into partial blocks having a vertical length of ¼ of anupper level block, where a block is partitioned into partial blockshaving a vertical length of ½ of an upper level block, where a block ispartitioned into partial blocks having a vertical length of ¾ of anupper level block, and the like. Accordingly, BT partitioninginformation may be represented as 0 to 6.

In FIG. 34, QT partitioning information and BT partitioning informationare indicated in a tree structure.

Based on the above description, a method for controlling the number ortype of intra-prediction modes in an encoding/decoding block and amethod for encoding/decoding the same will be described in detail.

FIG. 35 is a flowchart illustrating a procedure of controlling thenumber or type of prediction modes in an encoding device. In FIG. 35,each steps are connected as a series of flow, but it is not limited thateach steps is performed in the exemplified order. For example, when adetermination result on the number or type of intra-prediction modes ofa prediction block is not affected, the exemplified order may bechanged. For example, when there is no change in the number or type ofintra-prediction modes if the order of steps S3501 and S3502 is changed,the order may be changed. In addition, some of the steps shown in FIG.35 may be omitted. For example, if it is possible to control the numberor type of intra-prediction modes regardless of a shape of a predictionblock, step S3502 may be omitted.

In the present embodiment, a current encoding block may represent aprediction block or an encoding block including a prediction block.Hereinafter, the present invention will be described in detail withreference to FIG. 35.

In S3501, it has been shown that the number or type of intra-predictionmodes may be controlled according to a size of a current encoding block.In detail, the number of intra-prediction modes available for a currentencoding block may be variably determined according to a size of thecurrent encoding block. For example, the number of intra-predictionmodes available for the current encoding block may increase as a size ofthe current encoding block increases. For example, assuming that aminimum size of a prediction block is 4×4 and a maximum size is 256×256,when the size of the current encoding block is 4×4 or more and 32×32 orless, the number of intra-prediction modes available for the currentencoding block may be set to 35, or when the size of the currentencoding block is 64×64 or more and 256×256 or less, the number ofintra-prediction modes available for the current encoding block may beset to 67.

Alternatively, the number of intra-prediction modes available for acurrent encoding block may increase as a size of the current encodingblock decreases. For example, assuming that a minimum size of aprediction block is 4×4 and a maximum size is 256×256, when the size ofthe current encoding block is 4×4 or more and 32×32 or less, the numberof intra-prediction modes available for the current encoding block maybe set to 67, or when the size of the current encoding block is 64×64 ormore and 256×256 or less, the number of intra-prediction modes availablefor the current encoding block may be set to 35.

The number of intra-prediction modes available for a current encodingblock may be determined according to a comparison result of a size ofthe current encoding block with a reference size. Here, the referencesize may be signaled through an upper header, or may be derived as asame condition in an encoding device and a decoding device. For example,assuming that the reference size is 32×32, information on the referencesize may be defined by applying log function as ‘log₂ 32’, and may betransmitted through a bitstream. As the size of the current encodingblock is smaller or larger than the reference size, the number ofintra-prediction modes available for the current encoding block mayincrease. For example, when the size of the current encoding block is32×32, the number of intra-prediction modes available for the currentencoding block may be 19, when the size of the current encoding block is64×64 or more and 128×128 or less, the number of intra-prediction modesavailable for the current encoding block may be 35, and when the size ofthe current encoding block is 256×256, the number of intra-predictionmodes available for the current encoding block may be 67. When the sizeof the current encoding block is 16×16 or less and 8×8 or more, thenumber of intra-prediction blocks available for the current encodingblock is 35, and when the size of the current encoding block is 4×4, thenumber of intra-prediction blocks available for the current encodingblock is 67.

Alternatively, as the size of the current encoding block is smaller orlarger than the reference size, the number of intra-prediction modesavailable for the current encoding block may decrease. For example, whenthe size of the current encoding block is 32×32, the number ofintra-prediction modes available for the current encoding block may be67, when the size of the current encoding block is 64×64 or more and128×128 or less, the number of intra-prediction modes available for thecurrent encoding block may be 35, and when the size of the currentencoding block is 256×256, the number of intra-prediction modesavailable for the current encoding block may be 19. When the size of thecurrent encoding block is 16×16 or less and 8×8 or more, the number ofintra-prediction blocks available for the current encoding block is 35,and when the size of the current encoding block is 4×4, the number ofintra-prediction blocks available for the current encoding block is 19.

Regardless of a size of a current encoding block, the intra-predictionmode available for the current encoding block may include anon-directional intra-prediction mode (or a non-angular predictionmode). That is, regardless of a size of a current encoding block, thecurrent encoding block may be encoded using a non-directionalintra-prediction mode. In addition, the number of directional predictionmodes (i.e., angular prediction modes) available for the currentencoding block may vary depending on a size of the current encodingblock. As the number of intra-prediction modes available for the currentencoding block is decreased or increased, the number of directionalprediction modes available for the current encoding block may alsodecrease or increase.

When the number of directional prediction modes available for thecurrent encoding block decreases, the current encoding block may use aninteger unit directional prediction mode or a similar mode thereof.Here, the integer unit directional prediction mode means a mode in whichintra-prediction may be performed using an integer unit referencesample. Here, the integer unit reference sample may mean the referencesample itself, not an additional reference sample generated through aninterpolation of the reference sample. For example, the intra-predictionmode in a horizontal direction, a vertical direction, or a diagonaldirection may be an integer unit directional prediction mode.

In addition, a directional prediction mode available for the currentencoding block may be determined by partitioning an entire directionalprediction mode section by the number N of directional prediction modesto be used (N−1 equally partitioning).

FIG. 36 and FIG. 37 are diagrams illustrating examples in which 13directional prediction modes are available for the current encodingblock.

Referring to FIG. 36, intra-prediction modes available for the currentencoding block may be an integer unit directional prediction mode and adirectional prediction mode adjacent to the integer unit directionalprediction mode. For example, in FIG. 36, intra-prediction modes of avertical direction, a horizontal direction and three diagonaldirections, and intra-prediction modes (intra-prediction modes with anoffset of ±1) adjacent thereto are shown as available directionalprediction modes.

Referring to FIG. 37, directional prediction modes available for thecurrent encoding block may be 13 directional prediction modes allocatedat uniform intervals by partitioning an entire section of directionalprediction modes into 12 equal parts.

When the number of intra-prediction modes available to the currentprediction block increases, more intra-prediction modes adjacent to aninteger unit directional prediction mode may be used, or an entiresection of directional prediction modes may be partitioned into moreparts.

For example, FIG. 38 and FIG. 39 are diagrams illustrating examples inwhich there are 21 directional prediction modes available for thecurrent block.

In FIG. 38, for intra-prediction modes available for the currentencoding block, intra-prediction modes of a vertical direction, ahorizontal direction and three diagonal directions, and intra-predictionmodes (intra-prediction modes with an offset of ±2) adjacent thereto areshown as directional prediction modes available for the current encodingblocks.

In FIG. 39, it is shown that intra-prediction modes available for thecurrent encoding block are 21 directional prediction modes allocated atuniform intervals by partitioning an entire section of directionalprediction modes into 20 equal parts.

An encoding device may encode the number of intra-prediction modesavailable for each size of a prediction block, and may transmit theencoded number to a decoding device. Here, information indicating thenumber of intra-prediction modes available for each size of a predictionblock may be encoded in an upper header. For example, assuming that aminimum size of a prediction block is 4×4 and a maximum size is 256×256,and when it is determined that the number of intra-prediction modesavailable for a prediction block smaller than or equal to 32×32 block is64, a value (log₂ 64) which is obtained by applying log to the number ofavailable intra-prediction modes may be encoded and transmitted to adecoding device. When it is determined that the number ofintra-prediction modes available for a prediction block with 64×64 is32, a value (log₂32) which is obtained by applying log to the number ofavailable intra-prediction modes may be encoded, when it is determinedthat the number of intra-prediction modes available for a predictionblock with 128×128 is 16, a value (log₂ 16) which is obtained byapplying log to the number of available intra-prediction modes may beencoded, and when it is determined that the number of intra-predictionmodes available for a prediction block with 256×256 is 8, a value (log₂8) which is obtained by applying log to the number of availableintra-prediction modes may be encoded.

For additional example, the number of intra-prediction modes availablefor each size of a prediction block may be predetermined in an upperheader, the number of intra-prediction modes optimal for each predictionblock may be determined, and thus index information indicating thenumber of intra-prediction modes available in units of a predictionblock may be encoded. For example, when the number of intra-predictionmodes available for a 32×32 prediction block is 19, 35 or 67, an indexinformation indicating which one of 19, 35 or 67 is optimal for the32×32 prediction block may be encoded.

An encoding device may encode information indicating whether the numberor type of intra-prediction modes is to be adjusted according to a sizeof a prediction block. The encoded information may be transmitted to adecoding device through an upper header. Here, the information may be a1-bit flag, but is not limited thereto. The decoding device maydetermine in advance, based on the flag information, whether the numberor type of intra-prediction modes is adjusted for each size of aprediction block.

Even when information encoded in an upper header indicates that thenumber of available intra-prediction modes may be adjusted according toa size of a prediction block, intra-prediction in a conventional methodmay be performed for a current encoding block, or intra-prediction maybe performed by adjusting the number of available intra-prediction modesaccording to the size of the prediction block for the current encodingblock. Accordingly, when the information encoded in the upper headerindicates that the number of available intra-prediction modes may beadjusted according to the size of the prediction block, an encodingdevice may further encode, in units of a prediction block, informationindicating whether the prediction block is encoded according to aconventional method (i.e., using a fixed number of intra-predictionmodes) or the number of available intra-prediction modes is adjustedaccording to the size of the prediction block. Here, the encodedinformation may be a 1-bit flag, but is not limited thereto.

In S3502, it is shown that the number or type of intra-prediction modesmay be controlled according to a shape of a current encoding block. Indetail, the number of intra-prediction modes available for the currentencoding block may be variably determined according to a shape of thecurrent encoding block. For example, when the current block is anon-square block (e.g., a rectangle), it may be set for the currentblock that intra-prediction modes in horizontal direction may be usedmore than intra-prediction modes in vertical direction, orintra-prediction modes in vertical direction may be used more thanintra-prediction modes in horizontal direction.

Specifically, when a shape of a current encoding block is non-square,the number of intra-prediction modes in horizontal direction andintra-prediction modes in vertical direction available for the currentblock may be determined according to a ratio of width and height of thecurrent encoding block. For example, when the size of the currentencoding block is 8×16, since the height is twice the width of thecurrent encoding block, the number of horizontal intra-prediction modesmay be about twice the number of horizontal intra-prediction modesavailable for the current encoding block. For example, when the numberof directional intra-prediction modes available for the current codingblock is 25, the current encoding block may be set to use 16 horizontalintra-prediction modes and 9 vertical intra-prediction modes.

The number of intra-prediction modes available for a current codingblock may be determined by comparing a width or height of the currentcoding block with a predetermined threshold value. Here, the thresholdvalue may be signaled through an upper header. For example, a valueobtained by applying log (Log₂) to a threshold value may be signaledthrough an upper header. Alternatively, an encoding device and adecoding device may derive a threshold value under the same conditions.Here, the threshold value may be set for each of the width and theheight, or the same value may be used for the width and the height. Forexample, when a threshold value for a width is 32, and when the width ofthe current encoding block is less than the threshold value, the currentencoding block may use only ½N among N horizontal directionintra-prediction modes. For example, when the number of horizontaldirectional prediction mode is 33, the current coding block may use 17horizontal directional prediction modes.

Regardless of a shape of a current encoding block, intra predictionmodes available for the current encoding block may include anon-directional intra prediction mode (or a non-angular predictionmode). In addition, the number of directional prediction modes (i.e.,angular prediction modes) available for the current encoding block mayvary according to a shape of the current encoding block. As the numberof intra-prediction modes available for the current encoding blockdecreases or increases, the number of directional prediction modesavailable for the current encoding block may also decrease or increase.

Directional prediction modes available for a current encoding block maybe determined to be an integer unit directional prediction mode or asimilar mode. Alternatively, directional prediction modes available fora current encoding block may be determined by partitioning an entiresection of directional prediction modes by the number N of directionalprediction modes to be used (N−1 equally partitioned). This has beendescribed above with reference to FIG. 36 to FIG. 39, so that detaileddescription thereof will be omitted.

An encoding device may encode information indicating whether the numberor type of intra-prediction modes is to be adjusted according to a shapeof a prediction block. The encoded information may be transmitted to adecoding device through an upper header. Here, the information may be a1-bit flag, but is not limited thereto. The decoding device maydetermine in advance, based on the flag information, whether or not thenumber or type of intra-prediction modes is adjusted for each shape of aprediction block.

Even when information encoded in an upper header indicates that thenumber of available intra-prediction modes may be adjusted according toa shape of a prediction block, intra-prediction in a conventional methodmay be performed for a current encoding block, or intra-prediction maybe performed by adjusting the number of available intra-prediction modesaccording to the shape of the prediction block for the current encodingblock. Accordingly, when the information encoded in the upper headerindicates that the number of available intra-prediction modes may beadjusted according to the shape of the prediction block, an encodingdevice may further encode, in units of a prediction block, informationindicating whether the prediction block is encoded according to aconventional method (i.e., using a fixed number of intra-predictionmodes) or the number of available intra-prediction modes is adjustedaccording to the shape of the prediction block. Here, the encodedinformation may be a 1-bit flag, but is not limited thereto.

In S3503, it is shown that the number or type of intra-prediction modesmay be controlled according to a neighboring block of a current encodingblock. In detail, the number of intra-prediction modes available for acurrent encoding block may be determined according to intra-predictionmodes of neighboring blocks neighboring the current encoding block.

For example, referring to statistics of intra-prediction modes ofneighboring blocks of a current encoding block, when non-directionalprediction modes and directional prediction modes are mixed and a ratioof the non-directional prediction modes and the directional predictionmodes is equal to or greater than a threshold ratio or is equal to orsmaller than the threshold ratio, intra-prediction characteristic of thecurrent encoding block may be determined to be ambiguous. When it isdetermined that the intra-prediction characteristic of the currentencoding block is ambiguous, the number or type of intra-predictionmodes available for the current encoding block may not be changed.Accordingly, all intra-prediction modes may be used for the currentencoding block.

For example, referring to intra-prediction modes of neighboring blocksof a current block, when there are 9 non-directional modes and 8directional modes, and there are 4 horizontal modes and 4 vertical modesamong the directional modes, it is difficult to determine which of thenon-directional, vertical directional or horizontal directional mode isdesirable for the current encoding block. When it is difficult todetermine intra-prediction modes used mainly by neighboring predictionblocks because a ratio of non-directional prediction modes anddirectional prediction modes of the neighboring blocks neighboring thecurrent prediction block is close to 1:1, or when it is difficult todetermine main directionality of neighboring prediction blocks becausethe neighboring prediction blocks are encoded using directionalprediction mode but horizontal directional modes and verticaldirectional modes are mixed, the number or type of intra-predictionmodes available for the current encoding block may not be changed.

In addition, referring to statistics of intra-prediction modesneighboring a current encoding block, when it is determined thatnon-directional prediction modes are used more than directionalprediction modes by more than a threshold ratio, predictioncharacteristics of the current encoding block may be determined to be anon-directional mode. In this case, intra-prediction modes available forthe current encoding block may necessarily include a non-directionalmode, and may additionally include a predetermined number of directionalmodes. When neighboring blocks of the current encoding block are mostlyencoded through non-directional prediction modes, it is less likely thata contour having a specific directionality appears in the currentencoding block. Accordingly, even when using only non-directionalprediction modes, or using only non-directional prediction modes and apredetermined number of directional prediction modes (e.g., twoprediction modes of a vertical directional prediction mode and ahorizontal directional prediction mode), an optimal intra-predictionmode for the current encoding block may be identified.

Referring to statistics of intra-prediction modes neighboring a currentencoding block, when it is determined that directional prediction modesare used more than non-directional prediction modes by more than athreshold ratio, prediction characteristics of the current encodingblock may be determined to be a directional mode. When a ratio betweenhorizontal directional prediction modes and vertical directionalprediction modes for intra-prediction modes of neighboring blocks isskewed to one side (e.g., when horizontal directional prediction modesare used more than vertical directional prediction mode by a thresholdratio, when vertical directional prediction modes are used more thanhorizontal directional prediction mode by a threshold ratio, or thelike), intra-prediction modes available for the current encoding blockmay be configured using directional prediction modes more used amonghorizontal directional prediction modes and vertical directionalprediction modes. Here, intra-prediction modes available for the currentencoding block may further include non-directional prediction modes inaddition to horizontal directional or vertical directional predictionmodes.

For example, when intra-prediction modes neighboring a current encodingblock is all the directional prediction modes, and there are 11horizontal directional modes and 2 vertical directional mode amongintra-prediction modes of neighboring blocks, it is expected that thecurrent block may have characteristics of horizontal direction.Accordingly, an optimal intra-prediction mode for the current encodingblock may be determined using non-directional prediction modes andhorizontal directional prediction modes.

In the above example, a threshold ratio (a threshold ratio as a criteriafor directional modes and non-directional modes, a threshold ratio as acriteria for horizontal directional modes and vertical directional mode,and the like) may be signaled through an upper header. For example, avalue obtained by applying log (log 2) to a threshold ratio may betransmitted through an upper header.

Regardless of intra-prediction modes neighboring a current encodingblock, intra-prediction modes available for the current encoding blockmay include a non-directional intra-prediction mode (or a non-angularprediction mode). In addition, the number of directional predictionmodes (i.e., angular prediction modes) available for a current encodingblock may vary according to a pattern of using intra-prediction modesneighboring the current encoding block. As the number ofintra-prediction modes available for the current encoding blockdecreases or increases, the number of directional prediction modesavailable for the current encoding block may also decrease or increase.

Directional prediction modes available for a current encoding block maybe determined to be an integer unit directional prediction mode or asimilar mode. Alternatively, directional prediction modes available fora current encoding block may be determined by partitioning an entiresection of directional prediction modes by the number N of directionalprediction modes to be used (N−1 equally partitioned). This has beendescribed above with reference to FIG. 36 to FIG. 39, so that detaileddescription thereof will be omitted.

An encoding device may encode information indicating whether the numberor type of intra-prediction modes is to be adjusted according to apattern of using intra-prediction mode of neighboring blocks neighboringa prediction block. The encoded information may be transmitted to adecoding device through an upper header. Here, the information may be a1-bit flag, but is not limited thereto. The decoding device maydetermine in advance, based on the flag information, whether or not thenumber or type of intra-prediction modes is adjusted for each shape of aprediction block.

Even when information encoded in an upper header indicates that thenumber of available intra-prediction modes may be adjusted according toa pattern of using intra-prediction mode of neighboring blocksneighboring a prediction block, intra-prediction in a conventionalmethod may be performed for a current encoding block, orintra-prediction may be performed by adjusting the number of availableintra-prediction modes according to the pattern of usingintra-prediction mode of neighboring blocks for the current encodingblock. Accordingly, when the information encoded in the upper headerindicates that the number of available intra-prediction modes may beadjusted according to the pattern of using intra-prediction mode ofneighboring blocks, an encoding device may further encode, in units of aprediction block, information indicating whether the prediction block isencoded according to a conventional method (i.e., using a fixed numberof intra-prediction modes) or the number of available intra-predictionmodes is adjusted according to the pattern of using intra-predictionmode of neighboring blocks. Here, the encoded information may be a 1-bitflag, but is not limited thereto.

FIG. 35 has been described with reference to encoding procedure, it isalso possible in a decoding procedure to adjust the number ofintra-prediction modes available for a current block subjected todecoding. A decoding device may adjust the number of intra-predictionmodes available for a current decoding block in consideration of a size,a shape, a pattern of using intra-prediction mode of neighboringdecoding block, or the like, based on information signaled through abitstream.

When the number of intra-prediction modes available for a currentencoding block is determined, an encoding device may determine anintra-prediction mode of the current encoding block amongintra-prediction modes available for the current encoding block, and mayencode information on the determined intra-prediction mode. Hereinafter,a method of encoding/decoding an intra-prediction mode for a currentblock will be described in detail.

FIG. 40 is a flowchart illustrating a procedure of encoding an optimalintra-prediction mode for a current encoding block.

Referring to FIG. 40, firstly, an encoding device may determine an MPMcandidate for a current encoding block (S4001). Here, considering thatthe number of directional prediction modes available for the currentencoding block and those for neighboring blocks of the current encodingblock are different, the encoding device may set, for directionalprediction mode, a quantized directional prediction mode (or an angle ofa quantized directional prediction mode) as an MPM candidate.

For example, FIG. 41 is a diagram illustrating an example of setting anMPM candidate. In FIG. 41, it is exemplified that three MPM candidatesare used. In the example shown in FIG. 41, L may be an intra-predictionmode having a highest occurrence frequency among neighboring blocksadjacent to a left side of a current encoding block, or may be anintra-prediction mode of a neighboring block (or any neighboring block)at a predetermined position adjacent to a left side of a currentencoding block. Further, λ may be an intra-prediction mode having ahighest occurrence frequency among neighboring blocks adjacent to a topside a current encoding block, or may be an intra-prediction mode of aneighboring block (or any neighboring block) at a predetermined positionadjacent to a top side of a current encoding block.

The L, L−1, L+1 and A may represent an index of an intra-predictionmode. When the number of directional prediction modes available for thecurrent encoding block and those for neighboring blocks of the currentencoding block are different, a case may occur in which a directionalprediction mode used by a neighboring block is not available for thecurrent encoding block. For example, mode 18 among intra-predictionmodes available for the current encoding block may refer to a horizontaldirectional prediction mode, whereas, mode 18 among intra-predictionmodes available for a neighboring block may refer to a top leftdirectional prediction mode, not a horizontal directional mode.

In order to solve this inconsistency, when a non-directional predictionmode is assigned to an MPM candidate, index information may be used asit is, when a directional prediction mode is assigned to an MPMcandidate, a prediction angle corresponding to the directionalprediction mode may be assigned. As a quantized angle is set as an MPMcandidate, an encoding device may determine an intra-prediction mode fora current encoding block, based on whether a prediction angle of anoptimal directional prediction mode for the current encoding block isequal to a quantization angle included in MPM candidates. Accordingly,when an MPM candidate is a non-directional prediction mode, an index ofan intra-prediction mode such as L, L−1, L+1, A, etc. may be used as anMPM candidate, whereas when an MPM candidate is a directional predictionmode, an angle of an intra-prediction mode such as L′, (L−1)′, (L+1)′,A′, etc. may be used as an MPM candidate.

When a directional prediction mode matching with a prediction angle of aneighboring block is not available for a current encoding block,quantization that the prediction angle of the neighboring block isreduced to be most similar to a prediction angle of a directional modeavailable for the current prediction block may be performed.Accordingly, when an MPM candidate is a directional prediction mode, aMPM candidate indicating a quantized angle of a directional predictionmode such as L′, (L−1)′, (L+1)′, A′, etc. may be used.

For example, FIG. 42 and FIG. 43 are diagrams illustrating examples ofquantizing a prediction angle. FIG. 43 shows directional predictionmodes available for neighboring blocks adjacent to a current encodingblock, and FIG. 42 shows directional prediction modes available for thecurrent encoding block. Comparing FIG. 42 and FIG. 43, it may beconfirmed that directional prediction modes indicated by a dotted linein FIG. 43 are not available for the current encoding block.Accordingly, when a neighboring block is encoded using a directionalprediction mode indicated by the dotted line, a prediction angle of thedirectional prediction mode indicated by the dotted line may beconverted to a prediction angle of a most similar prediction mode amongdirectional prediction modes available for the current block and theconverted angle may be set as an MPM candidate.

In the above-described embodiment, it has been described that an MPMcandidate may be set as a prediction angle for a directional predictionmode, considering a case where the number of directional predictionmodes available for a current encoding block and those for neighboringblocks of the current encoding block are different.

For additional example, when the number of directional prediction modesavailable for a current encoding block and those for neighboring blocksof the current encoding block are equal, an MPM candidate may indicatean index of an intra-mode also for a directional prediction mode.Alternatively, when the number of directional prediction modes availablefor a current encoding block and those for neighboring blocks of thecurrent encoding block are different, the MPM candidate may be set toindicate an index of an intra-prediction mode also for a directionalprediction mode. In this case, a directional prediction mode of aneighboring block may be quantized (or converted) into an index of amode having the most similar direction among directional predictionmodes available for the current block.

FIG. 44 is a diagram illustrating another example of setting an MPMcandidate.

An encoding device may derive an MPM candidate for a current encodingblock based on neighboring blocks adjacent to the current encodingblock. Here, the neighboring block adjacent to the current encodingblock may include at least one of a block adjacent to a top side of thecurrent encoding block, a block adjacent to a left side of the currentencoding block and a block adjacent to a corner of the current encodingblock.

For example, FIG. 45 is a diagram illustrating an example of neighboringblocks used to derive an MPM candidate of a current encoding block.Referring to FIG. 45, in order to derive an MPM candidate of a currentencoding block, a left neighboring block A, a top neighboring block B, aleft bottom neighboring block C, a right top neighboring block D and aleft top neighboring block E may be used.

An encoding device may generate an MPM candidate according to a priorityshown in FIG. 44. Assuming that the number of MPM candidates of acurrent encoding block is 5, firstly, intra-prediction modes ofneighboring blocks may be added as MPM candidates in an order of aneighboring block A and a neighboring block B. Next, non-directionalmodes such as Planar mode and DC mode may be added as MPM candidates.Next, intra-prediction modes of neighboring blocks may be added as MPMcandidates in an order of the neighboring block C, the neighboring blockD and the neighboring block E.

When the number of MPM candidates does not reach a maximum number, andwhen there is a directional mode in MPM candidates that have beendetermined so far, an encoding device may add a mode (e.g., adirectional mode with an offset of ±1) having a direction similar to adirectional mode as an MPM candidate.

Nevertheless, when the number of MPM candidates does not reach themaximum number, a vertical mode, a horizontal mode, and a predictionmode in a diagonal direction (e.g., a prediction mode in a left bottomdirection (a prediction mode with index 2), a prediction mode in a lefttop direction, a prediction mode in a right top direction, or the like)may be added to MPM candidates.

In FIG. 45, it is shown that MPM candidates may be derived fromneighboring blocks adjacent to a current encoding block. In theembodiment shown in FIG. 41 and FIG. 44, an MPM candidate may be derivedbased on an intra-prediction mode of neighboring block not adjacent to acurrent encoding block, according to a size, a shape, or decoding stateof the current encoding block or a neighboring block adjacent to thecurrent encoding block.

For example, FIG. 46 is a diagram illustrating an example of deriving anMPM candidate from a neighboring block that is not adjacent to a currentencoding block.

When there are non-square blocks (e.g., a rectangular block having awidth larger than a height) continuously in a top direction of a currentencoding block, and a height of a top neighboring block adjacent to thecurrent encoding block is smaller than a height of the current encodingblock, an encoding device may predict that an intra-prediction mode ofthe top neighboring block is not the same as an intra-prediction mode ofthe current encoding block. Alternatively, when an intra-prediction modeof the neighboring block adjacent to the top side of the currentencoding block is one of vertical directional prediction modes, theencoding device may predict that an intra-prediction mode of the topneighboring block is not the same as an intra-prediction mode of thecurrent encoding block.

In this case, the encoding device may consider deriving additional MPMcandidates from at least one of blocks adjacent to the current encodingblock, i.e., a left, left top, right top and left bottom neighboringblocks. Alternatively, the encoding device may derive an additional MPMcandidate from a block adjacent to the neighboring block, which is notadjacent to the current encoding block. For example, in the embodimentshown in FIG. 23, the encoding device may derive an MPM candidate basedon, instead of a block adjacent to a top side of the current encodingblock (i.e., 1st top neighboring block), a second top block (i.e., 2ndtop neighboring block) or a block located further in top direction.Alternatively, the encoding device may consider an MPM candidate usingonly an intra-prediction mode of a neighboring block in a specificdirection other than the top direction.

When there are non-square blocks (e.g., a rectangular block having aheight larger than a width) continuously in a left direction of acurrent encoding block, and a width of a left neighboring block adjacentto the current encoding block is smaller than a width of the currentencoding block, an encoding device may predict that an intra-predictionmode of the left neighboring block is not the same as anintra-prediction mode of the current encoding block. Alternatively, whenan intra-prediction mode of the neighboring block adjacent to the leftside of the current encoding block is one of horizontal directionalprediction modes, the encoding device may predict that anintra-prediction mode of the left neighboring block is not the same asan intra-prediction mode of the current encoding block.

In this case, the encoding device may consider deriving additional MPMcandidates from at least one of blocks adjacent to the current encodingblock, i.e., a top, left top, right top and left bottom neighboringblocks. Alternatively, the encoding device may derive an additional MPMcandidate from a block adjacent to the neighboring block, which is notadjacent to the current encoding block. For example, in the embodimentshown in FIG. 46, the encoding device may derive an MPM candidate basedon, instead of a block adjacent to a left side of the current encodingblock (i.e., 1st left neighboring block), a second left block (i.e., 2ndleft neighboring block) or a block located further in left direction.Alternatively, the encoding device may consider an MPM candidate usingonly an intra-prediction mode of a neighboring block in a specificdirection other than the left direction.

When MPM candidates of the current encoding block is determined, it ispossible to determine whether there is an MPM candidate identical to anintra-prediction mode of the current encoding block by comparing theintra-prediction mode of the current encoding block with the MPMcandidates. The encoding device may encode information indicatingwhether there is an MPM candidate identical to the intra-prediction modeof the current encoding block, according to the determination result(S4002). For example, when there is an MPM candidate identical to theintra-prediction mode of the current encoding block, the information isencoded as true, and when there is no MPM candidate identical to theintra-prediction mode of the current encoding block, the information isencoded as false.

When it is determined that there is an MPM candidate identical to theintra-prediction mode of the current encoding block (S4003), theencoding device may encode index information specifying an MPM candidateidentical to the intra-prediction mode of the current encoding blockamong MPM candidates (S4004).

In addition, when it is determined that there is no MPM candidateidentical to the intra-prediction mode of the current encoding block(S4003), the encoding device may encode an intra-prediction mode optimalfor the current encoding block among intra-prediction modes excludingintra-prediction modes set as the MPM candidates (S4005). Specifically,among all the intra-prediction modes available for the current encodingblock, after excluding intra-prediction modes set as the MPM candidates,by allocating bits so as to represent residual intra-prediction modes,information corresponding to the intra-prediction mode of the currentencoding block among the residual prediction modes may be encoded.

When encoding residual intra-prediction modes, in allocating bits, it ispossible to allocate fixed bits so as to represent the residualintra-prediction modes, but it is also possible to divide the residualintra-prediction modes into N groups and to differently set allocationbits for each groups. For example, when the number of intra-predictionmodes available in the current encoding block is 67 and the number ofMPM candidates is 6, the number of residual intra-prediction modes is61. Here, when dividing the residual intra-prediction modes into twogroups (A, B), 16 intra-prediction modes may by allocated to the group Aand 45 intra-prediction modes may be allocated to the group B. Here,flag information for indicating to which group the intra-prediction modeof the current encoding block belongs may be encoded. For the group A,intra-prediction modes of the current encoding block may be encoded byallocating 4 bits, and for the group B, the group B may be divided againinto two sub-groups (B-1, B-2), 19 intra-prediction modes may beallocated to the group B-1, 26 intra-prediction modes may be allocatedto the group B-2, 5 bits may be allocated to the group B-1, and 6 bitsmay be allocated to the group B-2 to encode the intra-prediction mode ofthe current encoding block. The encoded information may be encoded andtransmitted to a decoding device through a bitstream.

Next, a description will be given of decoding the intra-prediction modefor a current decoding block in a decoding device.

FIG. 47 is a flowchart illustrating a procedure of decoding anintra-prediction mode for a current decoding block.

Referring to FIG. 47, a decoding device may determine an MPM candidatefor a current decoding block (S4701). The decoding device may determinethe MPM candidate for the current decoding block in consideration ofintra-prediction modes of neighboring blocks neighboring the currentdecoding block as in the encoding procedure described above.

Thereafter, the decoding device may decode, from a bitstream,information indicating whether there is an MPM candidate identical to anintra-prediction mode of the current decoding block among the MPMcandidates (S4702). The information may be a 1-bit flag, but is notlimited thereto.

When it is determined that there is an MPM candidate identical to theintra-prediction mode of the current decoding block (S4703), thedecoding device may decode index information specifying an MPM candidateidentical to the intra-prediction mode of the current decoding blockamong the MPM candidates (Step S4704).

In addition, when it is determined that there is no MPM candidateidentical to the intra-prediction mode of the current decoding block(S4703), the decoding device may decode residual prediction modeinformation indicating a prediction mode optimal for the currentdecoding block among residual intra-prediction modes excludingintra-prediction modes set as the MPM candidates.

In the above-described example, an intra-prediction mode of a currentencoding/decoding block is determined using MPM candidates, but theintra-prediction mode of the current encoding/decoding block may bedetermined without using the MPM candidates. In this case, informationspecifying the intra-prediction mode of the current encoding/decodingblock may be transmitted to the decoding device through a bitstream.

Although the exemplary methods of this disclosure are represented by aseries of steps for clarity of explanation, they are not intended tolimit the order in which the steps are performed, and if necessary, eachstep may be performed simultaneously or in a different order. In orderto implement the method according to the present disclosure, it ispossible to include other steps to the illustrative steps additionally,exclude some steps and include remaining steps, or exclude some stepsand include additional steps.

The various embodiments of the disclosure are not intended to beexhaustive of all possible combination, but rather to illustraterepresentative aspects of the disclosure, and the features described inthe various embodiments may be applied independently or in a combinationof two or more.

In addition, various embodiments of the present disclosure may beimplemented by hardware, firmware, software, or a combination thereof. Acase of hardware implementation may be performed by one or moreapplication specific integrated circuits (ASICs), digital signalprocessors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), a general processor, a controller, a microcontroller, amicroprocessor, and the like.

The scope of the present disclosure is to encompass software ormachine-executable instructions (e.g., operating system, applications,firmware, instructions, and the like) by which operations according tomethod of various embodiments are executed on a device or a computer,and non-transitory computer-readable media executable on the device orthe computer, on which such software or instructions are stored.

INDUSTRIAL APPLICABILITY

The present invention may be applied to processing image signal.

1. A method of decoding an image signal, comprising: receiving abitstream including a coded picture of the image signal; deriving anintra prediction mode of a current coding block in the coded pictureamong intra prediction modes available for the current coding block; andperforming intra prediction based on the derived intra prediction modeto generate a prediction block of the current coding block, wherein theintra prediction modes available for the current coding block isclassified into a plurality of groups, wherein the intra prediction modeof the current coding block is derived from one of the plurality ofgroups, and wherein a number of the groups is an integer greater than orequal to
 3. 2. The method of claim 1, the method further comprising:obtaining, from a bitstream, one or more flags specifying a group towhich the intra prediction mode of the current coding block belongsamong the plurality of groups; and determining, based on the one or moreflags, the group to which the intra prediction mode of the currentcoding block belongs.
 3. The method of claim 2, wherein a maximum numberof the flags obtained for the current coding block is equal to a valueresulting from subtracting one from the number of groups.
 4. The methodof claim 1, wherein one of the groups includes only five MPM (mostprobable mode) candidates for the intra prediction of the current codingblock.
 5. The method of claim 4, wherein the MPM candidates are derivedbased on an intra prediction mode of a neighboring block adjacent to thecurrent coding block, and wherein the neighboring block includes atleast one of a left neighboring block or a top neighboring block of thecurrent coding block.
 6. The method of claim 5, wherein the topneighboring block is representative of a right-most block of topneighboring blocks adjacent to the current coding block, and is used toderive the MPM candidates of the current coding block.
 7. The method ofclaim 5, wherein the left neighboring block is representative of abottom-most block of left neighboring blocks adjacent to the currentcoding block, and is used to derive the MPM candidates of the currentcoding block.
 8. A method of encoding an image signal, comprising:receiving a picture of the image signal; deriving an intra predictionmode of a current coding block in the picture among intra predictionmodes available for the current coding block; and performing intraprediction based on the derived intra prediction mode to generate aprediction block of the current coding block, wherein the intraprediction modes available for the current coding block is classifiedinto a plurality of groups, wherein the intra prediction mode of thecurrent coding block is derived from one of the plurality of groups, andwherein a number of the groups is an integer greater than or equal to 3.9. A non-transitory computer-readable medium for storing data associatedwith an image signal, comprising: a data stream encoded by an encodingmethod, wherein the encoding method comprises: receiving a picture ofthe image signal; deriving an intra prediction mode of a current codingblock in the picture among intra prediction modes available for thecurrent coding block; and performing intra prediction based on thederived intra prediction mode to generate a prediction block of thecurrent coding block, wherein the intra prediction modes available forthe current coding block is classified into a plurality of groups,wherein the intra prediction mode of the current coding block is derivedfrom one of the plurality of groups, and wherein a number of the groupsis an integer greater than or equal to 3.